Oxygen ' onMouseout='HidePop("67806")' href="http://www.absoluteastronomy.com/topics/Greek_language">Greek
Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
roots ὀξύς (oxys) (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the
elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
with
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
8 and represented by the symbol
O. It is a member of the
chalcogenThe chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
group on the
periodic tableThe periodiс table of the chemical elements is a tabular display of the chemical elements...
, and is a highly reactive
nonmetalNonmetal, or non-metal, is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal...
lic
period 2 elementA period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical...
that readily forms
compoundsA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
(notably
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s) with almost all other elements. At standard temperature and pressure two atoms of the element
bindA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
to form dioxygen, a colorless, odorless, tasteless diatomic
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
with the formula . Oxygen is the
third most abundantThe abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. Abundance may be variously measured by the mass-fraction , or mole-fraction , or by volume fraction...
element in the universe by mass after
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
and
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
and the
most abundant-Earth bulk continental crust and upper continental crust:*C1 — Crust: CRC Handbook*C2 — Crust: Kaye & Laby*C3 — Crust: Greenwood*C4 — Crust: Ahrens *C5 — Crust: Ahrens...
element by mass in the Earth's crust. Diatomic oxygen gas constitutes 20.9% of the volume of
airThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
.
All major classes of structural molecules in living organisms, such as
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s,
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s, and
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s, contain oxygen, as do the major
inorganic compoundTraditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin...
s that comprise animal shells, teeth, and bone. Oxygen in the form of is produced from water by
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
,
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
and plants during
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
and is used in
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
for all complex life. Oxygen is toxic to
obligately anaerobic organismsObligate anaerobes are anaerobic organisms that fail to grow in the presence of oxygen.-Metabolism:Obligate anaerobes die in presence of oxygen due to the absence of the enzymes superoxide dismutase and catalase, which would convert the lethal superoxide formed in their cells due to the presence...
, which were the dominant form of
early lifeThe evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved. It stretches back over , possibly as far as , and evolution continues, even in humans. All present-day organisms use the same large set of complex chemical reactions, which indicates that...
on Earth until began to accumulate in the atmosphere 2.5 billion years ago. Another form (
allotropeThere are several known allotropes of oxygen:*Free radicals O1 - unstable*dioxygen, O2 - colorless*ozone, O3 - blue*tetraoxygen, O4 - metastable...
) of oxygen,
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
, helps protect the biosphere from ultraviolet radiation with the high-altitude
ozone layerThe ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here...
, but is a pollutant near the surface where it is a by-product of
smogSmog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide...
. At even higher
low earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
altitudes atomic oxygen is a significant presence and a cause of
erosion for spacecraftCorrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet light and x-rays, high-energy charged particles...
.
Oxygen was independently discovered by
Carl Wilhelm ScheeleCarl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
, in
UppsalaUppsala is the capital of Uppsala County and the fourth largest city of Sweden with 144,839 inhabitants....
, in 1773 or earlier, and
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
in
WiltshireWiltshire is a ceremonial county in the south west of England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers 3,485 km²...
, in 1774, but Priestley is often given priority because his publication came out in print first. The name
oxygen was coined in 1777 by
Antoine LavoisierAntoine-Laurent de Lavoisier ; ), the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology...
, whose experiments with oxygen helped to discredit the then-popular
phlogiston theoryThe phlogiston theory , first stated in 1667 by Johann Joachim Becher, is a defunct scientific theory that posited the existence of a fire-like element called "phlogiston" that was contained within combustible bodies, and released during combustion...
of
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. Oxygen is produced industrially by
fractional distillationFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
of liquefied air, use of
zeoliteZeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
s to remove
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
and
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
from air,
electrolysis of waterElectrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water...
and other means. Uses of oxygen include the production of steel, plastics and textiles;
rocket propellantRocket propellant is mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot...
;
oxygen therapyOxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
; and life support in aircraft, submarines,
spaceflightHuman spaceflight is spaceflight with a human crew and possibly passengers. This makes it unlike robotic space probes or remotely-controlled satellites...
and
divingUnderwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
.
Structure
At standard temperature and pressure, oxygen is a colorless, odorless gas with the
molecularA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
formula , in which the two oxygen atoms are
chemically bondedA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
to each other with a spin triplet
electron configurationIn atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
. This bond has a
bond orderBond order is the number of chemical bonds between a pair of atoms. For example, in diatomic nitrogen N≡N the bond order is 3, while in acetylene H−C≡C−H the bond order between the two carbon atoms is also 3, and the C−H bond order is 1. Bond order gives an indication to the stability of a bond. In...
of two, and is often simplified in description as a
double bondA double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
or as a combination of one two-electron bond and two three-electron bonds.
Triplet oxygenTriplet oxygen is the ground state of the oxygen molecule. The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals...
(not to be confused with
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
, ) is the ground state of the molecule. The electron configuration of the molecule has two unpaired electrons occupying two
degenerateDegenerate orbitals for electrons in an atomic subshell are orbitals at identical energy levels. These are important in physical chemistry because they affect the ways electrons fill atoms . For example, all the 3p orbitals have same energy level, and so do all the 5d orbitals. Each orbital is...
molecular orbitalIn chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The use of the term...
s. These orbitals are classified as
antibondingAntibonding is a type of chemical bonding. An antibonding orbital is a form of molecular orbital that is located outside the region of two distinct nuclei. The overlap of the constituent atomic orbitals is said to be 'out of phase' and as such the electrons present in each antibonding orbital are...
(weakening the bond order from three to two), so the diatomic oxygen bond is weaker than the diatomic
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
triple bond in which all bonding molecular orbitals are filled, but some antibonding orbitals are not.
In normal triplet form, molecules are
paramagneticParamagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability of ≥1 .The magnetic moment induced by the applied field is linear in the field...
—they form a magnet in the presence of a magnetic field—because of the
spinIn particle physics and quantum mechanics, spin is a fundamental characteristic property of elementary particles including the force carriers , composite particles , and atomic nuclei....
magnetic momentThe magnetic moment of a system is a measure of the strength and the direction of its magnetism. More technically , the term magnetic moment of a system usually refers to its magnetic dipole moment, and quantifies the contribution...
s of the unpaired electrons in the molecule, and the negative exchange energy between neighboring molecules. Liquid oxygen is attracted to a
magnetA magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets.A permanent magnet is an object made from a...
to a sufficient extent that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet.
Singlet oxygenSinglet oxygen is the common name used for the diamagnetic form of molecular oxygen , which is less stable than the normal triplet oxygen. Because of its unusual properties, singlet oxygen can persist for over an hour at room temperature, depending on the environment...
, a name given to several higher-energy species of molecular in which all the electron spins are paired, is much more reactive towards common
organic moleculesAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the
troposphereThe troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor and aerosols....
by the photolysis of ozone by light of short wavelength, and by the immune system as a source of active oxygen.
CarotenoidCarotenoids are organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria....
s in photosynthetic organisms (and possibly also in animals) play a major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues.
Allotropes
The common
allotropeAllotropy or allotropism is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner...
of elemental oxygen on Earth is called dioxygen, . It has a bond length of 121
pmA picometre is a unit of length in the metric system, equal to one trillionth or one billionth , i.e. of a meter, which is the current SI base unit of length...
and a bond energy of 498
kJ·mol-1The joule per mole is an SI derived unit of energy per amount of material. Energy is measured in joules, and the amount of material is measured in moles....
. This is the form that is used by complex forms of life, such as animals, in cellular respiration (see Biological role) and is the form that is a major part of the Earth's atmosphere (see Occurrence). Other aspects of are covered in the remainder of this article.
Trioxygen is usually known as
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
and is a very reactive allotrope of oxygen that is damaging to lung tissue. Ozone is produced in the upper atmosphere when combines with atomic oxygen made by the splitting of by
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(UV) radiation. Since ozone absorbs strongly in the UV region of the
spectrumThe electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, the
ozone layerThe ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here...
of the upper atmosphere functions as a protective radiation shield for the planet. Near the Earth's surface, however, it is a
pollutantAir pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment, into the atmosphere....
formed as a by-product of automobile exhaust. The metastable molecule
tetraoxygenThe tetraoxygen molecule , also called oxozone was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxygen to obey Curie's law...
was discovered in 2001, and was assumed to exist in one of the six phases of
solid oxygenSolid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K . Solid oxygen O
2, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red .Oxygen molecules have attracted attention because of the...
. It was proven in 2006 that this phase, created by pressurizing to 20
GPaThe pascal is the SI derived unit of pressure, stress, Young's modulus and tensile strength. It is a measure of force per unit area, defined as one newton per square metre...
, is in fact a rhombohedral
clusterIn chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
. This cluster has the potential to be a much more powerful
oxidizerAn oxidizing agent can be defined as either:#a chemical compound that readily transfers oxygen atoms, or#a substance that gains electrons in a redox chemical reaction...
than either or and may therefore be used in rocket fuel. A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa and it was shown in 1998 that at very low temperatures, this phase becomes
superconductingSuperconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field . It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral...
.
Physical properties
Oxygen is more
solubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure...
in water than nitrogen; water contains approximately 1 molecule of for every 2 molecules of , compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L
−1) dissolves at 0 °C than at 20 °C (7.6 mg·L
−1). At 25 °C and of air, freshwater contains about 6.04
milliliterThe litre or liter is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case . The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau...
s (mL) of oxygen per
liter
, whereas
seawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
contains about 4.95 mL per liter. At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for water and 7.2 mL (45% more) per liter for sea water.
Oxygen condenses at 90.20
KThe kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero kelvin...
(−182.95 °C, −297.31 °F), and freezes at 54.36 K (−218.79 °C, −361.82 °F). Both
liquidLiquid oxygen is a form of the element oxygen. It has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horse shoe magnet...
and
solidSolid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K . Solid oxygen O
2, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red .Oxygen molecules have attracted attention because of the...
are clear substances with a light
sky-blueDiffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. It is also called skylight, diffuse skylight, or sky radiation and is the reason for changes in the colour of the sky...
color caused by absorption in the red (in contrast with the blue color of the sky, which is due to
Rayleigh scatteringRayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light, which may be individual atoms or molecules. It can occur when light travels in transparent solids and liquids, but is most prominently seen in gases...
of blue light). High-purity liquid is usually obtained by the
fractional distillationFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
of liquefied air; Liquid oxygen may also be produced by condensation out of air, using liquid nitrogen as a coolant. It is a highly reactive substance and must be segregated from combustible materials.
Isotopes and stellar origin
Naturally occurring oxygen is composed of three stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s,
16O,
17O, and
18OOxygen-18 is a natural, stable isotope of oxygen and one of the environmental isotopes.18O is an important precursor for the production of fluorodeoxyglucose used in positron emission tomography...
, with
16O being the most abundant (99.762%
natural abundanceIn chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass of these isotopes is the atomic weight listed for the element in the periodic table...
).
Most
16O is
synthesizedNucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons . It is thought that the primordial nucleons themselves were formed from the quark-gluon plasma from the Big Bang as it cooled below two trillion degrees...
at the end of the
helium fusionHelium fusion is a kind of nuclear fusion, with the nuclei involved being helium.The fusion of helium-4 nuclei is known as the triple-alpha process, because fusion of just two helium nuclei only produces beryllium-8, which is unstable and breaks back down to two helium nuclei with a half life of...
process in
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
s but some is made in the
neon burning processThe neon burning process is a set of nuclear fusion reactions that take place in massive stars . Neon burning requires high temperatures and densities ....
.
17O is primarily made by the burning of hydrogen into
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
during the
CNO cycleThe CNO cycle , or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain. Theoretical models show that the CNO cycle is the dominant source of energy in stars heavier than about 1.5 times the mass...
, making it a common isotope in the hydrogen burning zones of stars. Most
18O is produced when
14NNitrogen-14 is a stable, non-radioactive isotope of the chemical element nitrogen.Nitrogen-14 comprises approximately 99% of all naturally formed nitrogen. It is the source of naturally-occurring carbon-14, which is created when cosmic radiation interacts with nitrogen-14 in the upper atmosphere. ...
(made abundant from CNO burning) captures a
4HeHelium-4 is a non-radioactive and light isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. The total spin of...
nucleus, making
18O common in the helium-rich zones of stars.
Fourteen radioisotopes have been characterized, the most stable being
15O with a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of 122.24 seconds (s) and
14O with a half-life of 70.606 s. All of the remaining
radioactiveRadioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter...
isotopes have half-lives that are less than 27 s and the majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than
16O is
β+ decayPositron emission is a type of beta decay, sometimes referred to as "beta plus" . In beta plus decay, a proton is converted, via the weak force, to a neutron, a positron , and a neutrino.Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40,...
to yield nitrogen, and the most common mode for the isotopes heavier than
18O is
beta decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
to yield
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
.
Occurrence
Oxygen is the most abundant chemical element, by mass, in our biosphere, air, sea and land.
Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. About 0.9% of the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
's mass is oxygen. Oxygen constitutes 49.2% of the Earth's crust by mass and is the major component of the world's oceans (88.8% by mass). Oxygen gas is the second most common component of the
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, taking up 21.0% of its volume and 23.1% of its mass (some 10
15 tonnes). Earth is unusual among the planets of the
Solar SystemThe Solar System consists of the Sun and those celestial objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago...
in having such a high concentration of oxygen gas in its atmosphere:
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
(with 0.1% by volume) and
VenusVenus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6...
have far lower concentrations. However, the surrounding these other planets is produced solely by ultraviolet radiation impacting oxygen-containing molecules such as carbon dioxide.
The unusually high concentration of oxygen gas on Earth is the result of the
oxygen cycleThe oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere , the biosphere , and the lithosphere...
. This
biogeochemical cycleIn ecology and Earth science, a biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth...
describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, the
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
, and the
lithosphereThe lithosphere is the rigid outermost shell of a rocky planet.- Earth's lithosphere :...
. The main driving factor of the oxygen cycle is
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
, which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while
respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
and
decayDecomposition is the process by which tissues of a dead organism break down into simpler forms of matter. The process is essential for new growth and development of living organisms because it recycles the finite matter that occupies physical space in the biome. Bodies of living organisms begin to...
remove it from the atmosphere. In the present equilibrium, production and consumption occur at the same rate of roughly 1/2000th of the entire atmospheric oxygen per year.
Free oxygen also occurs in solution in the world's water bodies. The increased solubility of at lower temperatures (see Physical properties) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content.
Polluted waterWater pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater. All water pollution affects organisms and plants that live in these water bodies and in almost all cases the effect is damaging either to individual species and populations but also to the natural...
may have reduced amounts of in it, depleted by decaying algae and other biomaterials (see
eutrophicationEutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem...
). Scientists assess this aspect of water quality by measuring the water's
biochemical oxygen demandBiochemical oxygen demand or BOD is a chemical procedure for determining the rate of uptake of dissolved oxygen by the rate biological organisms in a body of water use up oxygen. It is not a precise quantitative test, although it is widely used as an indication of the quality of water.BOD can be...
, or the amount of needed to restore it to a normal concentration.
Photosynthesis and respiration
In nature, free oxygen is produced by the light-driven splitting of water during oxygenic
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
.
Green algaeThe green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
and
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
in marine environments provide about 70% of the free oxygen produced on earth and the rest is produced by terrestrial plants.
A simplified overall formula for photosynthesis is:
-
- 6 + 6 + photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s → + 6 (or simply carbon dioxide + water + sunlight → glucose + dioxygen)
Photolytic
oxygen evolutionOxygen evolution is the process of generating molecular oxygen through chemical reaction. Mechanisms of oxygen evolution include the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and...
occurs in the thylakoid membranes of photosynthetic organisms and requires the energy of four
photonIn physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s. Many steps are involved, but the result is the formation of a
protonThe proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H
+...
gradient across the thylakoid membrane, which is used to synthesize
ATPAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
via
photophosphorylationThe production of ATP using the energy of sunlight is called photophosphorylation. Only two sources of energy are available to living organisms: sunlight and oxidation-reduction reactions...
. The remaining after oxidation of the water molecule is released into the atmosphere.
Molecular dioxygen, , is essential for cellular respiration in all
aerobic organismAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. -Types:*Obligate aerobes require oxygen for aerobic cellular respiration...
s. Oxygen is used in
mitochondriaIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
to help generate
adenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
(ATP) during
oxidative phosphorylationOxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that...
. The reaction for aerobic respiration is essentially the reverse of photosynthesis and is simplified as:
-
- + 6 → 6 + 6 + 2880 kJ·mol-1
In
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s, is
diffusedMolecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material...
through membranes in the lungs and into
red blood cellRed blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries. The cells are filled with hemoglobin, a...
s.
HemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
binds , changing its color from bluish red to bright red. Other animals use
hemocyaninHemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...
(
molluscMolluscs
[Spelled mollusk in the USA, see reasons given in Rosenberg's ; for the spelling "mollusc" see the reasons given by .] are animals belonging to the phylum Mollusca. There are around 93,000 recognized extant species, making it the largest marine phylum with about 23% of...
s and some
arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s) or
hemerythrinHemerythrin is an oligomeric protein responsible for oxygen transportation in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm, magelona. Recently, hemerythrin was discovered in methanotrophic bacterium Methylococcus capsulatus...
(
spiderSpiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s and
lobsterClawed lobsters compose a family of large marine crustaceans. Lobsters are economically important as seafood, forming the basis of a global industry that nets US$31.8 billion in trade annually....
s). A liter of blood can dissolve 200 cm
3 of .
Reactive oxygen speciesReactive oxygen species are free radicals that contain the oxygen atom. They are very small molecules that include oxygen ions and peroxides and can be either inorganic or organic. They are highly reactive due to the presence of unpaired valence shell electrons.ROS form as a natural byproduct of...
, such as
superoxideSuperoxide is an anion with the chemical formula O
2−. It is important as the product of the one-electron reduction of dioxygen O
2, which occurs widely in nature...
ion and
hydrogen peroxideHydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...
, are dangerous by-products of oxygen use in organisms. Parts of the
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
of higher organisms, however, create peroxide, superoxide, and singlet oxygen to destroy invading microbes. Reactive oxygen species also play an important role in the
hypersensitive responseThe hypersensitive response is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens. The HR is characterized by the rapid death of cells in the local region surrounding an infection. The HR serves to restrict the growth and spread of pathogens to other parts of...
of plants against pathogen attack.
An adult human in rest
inhalesBreathing is the process that takes oxygen in and carbon dioxide out of the body. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose...
1.8 to 2.4 grams of oxygen per minute. This amounts to more than 6 billion tonnes of oxygen inhaled by humanity per year.
Build-up in the atmosphere
Free oxygen gas was almost nonexistent in
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
before photosynthetic
archaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
and
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
evolved. Free oxygen first appeared in significant quantities during the
PaleoproterozoicThe Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
era (between 2.5 and 1.6 billion years ago). At first, the oxygen combined with dissolved
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
in the oceans to form
banded iron formationBanded iron formations are a distinctive type of rock often found in primordial sedimentary rocks. The structures consist of repeated thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...
s. Free oxygen started to gas out of the oceans 2.7 billion years ago, reaching 10% of its present level around 1.7 billion years ago.
The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have driven most of the
anaerobic organismAn anaerobic organism or anaerobe is any organism that does not require oxygen for growth and may even die in its presence. There are three types: obligate anaerobes, which cannot use oxygen for growth and are even harmed by it; aerotolerant organisms, which cannot use oxygen for growth, but...
s then living to
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
during the
oxygen catastropheThe Great Oxidation Event was a major environmental change around associated with the appearance of free oxygen in the atmosphere....
about 2.4 billion years ago. However,
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
using enables
aerobic organismAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. -Types:*Obligate aerobes require oxygen for aerobic cellular respiration...
s to produce much more ATP than anaerobic organisms, helping the former to dominate Earth's
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
. Photosynthesis and cellular respiration of allowed for the evolution of
eukaryotic cellEukaryotic Cell is an academic journal published by the American Society for Microbiology. The title is commonly abbreviated EC and the ISSN is 1535-9778 for the print version, and 1535-9786 for the electronic version....
s and ultimately complex multicellular organisms such as plants and animals.
Since the beginning of the
CambrianThe Cambrian is the first geological period of the Paleozoic era, lasting from ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux...
era 540 million years ago, levels have fluctuated between 15% and 30% by volume. Towards the end of the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
era (about 300 million years ago) atmospheric levels reached a maximum of 35% by volume, which may have contributed to the large size of insects and amphibians at this time. Human activities, including the burning of 7 billion
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s of
fossil fuelFossil fuels or mineral fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s each year have had very little effect on the amount of free oxygen in the atmosphere. At the current rate of photosynthesis it would take about 2,000 years to regenerate the entire in the present atmosphere.
Early experiments
One of the first known experiments on the relationship between
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and air was conducted by the second century BCE
GreekAncient Greece is the civilisation belonging to the period of Greek history lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman conquest of Greece after the Battle of Corinth. It is generally considered to be the seminal culture which provided the...
writer on mechanics,
Philo of ByzantiumPhilo of Byzantium , also known as Philo Mechanicus, a Greek writer on mechanics, flourished during the latter half of the 2nd century B.C...
. In his work
Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck.
Philo incorrectly surmised that parts of the air in the vessel were converted into the
classical elementMany philosophies and worldviews have used a set of archetypal classical elements, most developed sets of the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based...
fireFire has been an important part of all cultures and religions, from pre-history to modern day, and was vital to the development of civilization. It has been regarded in many different fashions throughout history.-Greek and Roman Tradition:...
and thus were able to escape through pores in the glass. Many centuries later
Leonardo da VinciLeonardo di ser Piero da Vinci was an Italian polymath, scientist, mathematician, engineer, inventor, anatomist, painter, sculptor, architect, botanist, musician and writer....
built on Philo's work by observing that a portion of air is consumed during combustion and
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
.
In the late 17th century,
Robert BoyleRobert Boyle was a natural philosopher, chemist, physicist, inventor, and gentleman scientist, also noted for his writings in theology. He is best known for the formulation of Boyle's law...
proved that air is necessary for combustion. English chemist
John MayowJohn Mayow FRS was a chemist, physician, and physiologist who is remembered today for conducting early research into respiration and the nature of air...
refined this work by showing that fire requires only a part of air that he called
spiritus nitroaereus or just
nitroaereus.
In one experiment he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
and combustion.
Mayow observed that
antimonyAntimony is a chemical element with the symbol Sb and atomic number 51. A metalloid, antimony has four allotropic forms. The stable form of antimony is a blue-white metalloid. Yellow and black antimony are unstable non-metals...
increased in weight when heated, and inferred that the nitroaereus must have combined with it. He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work
Tractatus duo in the tract "De respiratione".
Phlogiston theory
Robert HookeRobert Hooke, FRS was an English natural philosopher, architect and polymath who played an important role in the scientific revolution, through both experimental and theoretical work....
,
Ole BorchOle Borch was a Danish scientist, physician, grammarian, and poet, most famous today for being the teacher at the Vor Frue Skole in Copenhagen of Nicholas Steno. Borch had studied medicine at the University of Copenhagen and distinguished himself in the plague of 1654, when a third of...
,
Mikhail LomonosovMikhail Vasilyevich Lomonosov was a Russian polymath, scientist and writer, who made important contributions to literature, education, and science. Among his discoveries was the atmosphere of Venus. His spheres of science were natural science, chemistry, physics, mineralogy, history, art,...
, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as an element. This may have been in part due to the prevalence of the philosophy of
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
called the phlogiston theory, which was then the favored explanation of those processes.
Established in 1667 by the German alchemist
J. J. BecherJohann Joachim Becher , was a German physician, alchemist, precursor of chemistry, scholar and adventurer, best known for his development of the phlogiston theory and his advancement of Austrian cameralism....
, and modified by the chemist
Georg Ernst StahlGeorg Ernst Stahl , was a German chemist and physician.He was born at Ansbach. Having graduated in medicine at the University of Jena in 1683, he became court physician to Duke Johann Ernst of Sachsen Weimar in 1687...
by 1731,
phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or
calxCalx is a residual substance, sometimes in the form of a fine powder, that is left when a metal or mineral combusts or is calcinated due to heat.Calx, especially of a metal, is now known as an oxide...
.
Highly combustible materials that leave little
residueIn chemistry, residue refers to the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group....
, such as wood or coal, were thought to be made mostly of phlogiston; whereas non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. The fact that a substance like wood actually
gains overall weight in burning was hidden by the buoyancy of the gaseous combustion products. Indeed one of the first clues that the phlogiston theory was incorrect was that metals, too, gain weight in rusting (when they were supposedly losing phlogiston).
Discovery
Oxygen was first discovered by
SwedishSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
pharmacist
Carl Wilhelm ScheeleCarl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
. He had produced oxygen gas by heating mercuric oxide and various
nitrateIn inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates.-Chemical properties:...
s by about 1772. Scheele called the gas 'fire air' because it was the only known supporter of combustion. He wrote an account of this discovery in a manuscript he titled
Treatise on Air and Fire, which he sent to his publisher in 1775. However, that document was not published until 1777.
In the meantime, an experiment was conducted by the
BritishThe Kingdom of Great Britain, also known as the United Kingdom of Great Britain, was a sovereign state in northwest Europe, in existence from 1707 to 1801...
clergyman
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
on August 1, 1774 focused sunlight on
mercuric oxideMercury oxide, also called mercuric oxide or simply mercury oxide, has a formula of HgO and a formula weight of 216.6. It has a red or orange color. Mercury oxide is a solid at room temperature and pressure...
(HgO) inside a glass tube, which liberated a gas he named 'dephlogisticated air'. He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air" which was included in the second volume of his book titled
Experiments and Observations on Different Kinds of AirExperiments and Observations on Different Kinds of Air is a six-volume work published by eighteenth-century British polymath Joseph Priestley which reports a series of his experiments on "airs" or gases, most notably his discovery of oxygen gas .-Airs:While working as a companion for Lord...
. Because he published his findings first, Priestley is usually given priority in the discovery.
The noted French chemist
Antoine Laurent LavoisierAntoine-Laurent de Lavoisier ; ), the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology...
later claimed to have discovered the new substance independently. However, Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele also posted a letter to Lavoisier on September 30, 1774 that described his own discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of the letter was found in Scheele's belongings after his death).
Lavoisier's contribution
What Lavoisier did indisputably do (although this was disputed at the time) was to conduct the first adequate quantitative experiments on oxidation and give the first correct explanation of how combustion works. He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
.
In one experiment, Lavoisier observed that there was no overall increase in weight when
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4...
and air were heated in a closed container. He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book
Sur la combustion en général, which was published in 1777. In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and
azote (Gk.
"lifeless"), which did not support either.
Azote later became
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
in English, although it has kept the name in French and several other European languages.
Lavoisier renamed 'vital air' to
oxygène in 1777 from the
GreekAncient Greek is the historical stage in the development of the Greek language spanning across the Archaic , Classical , and Hellenistic periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek...
roots
(oxys) (
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
, literally "sharp," from the taste of acids) and
-γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. Chemists eventually determined that Lavoisier was wrong in this regard, but by that time it was too late, the name had taken. Actually, the gas that could more appropriately have been given the description, "acid producer," is hydrogen.
Oxygen entered the English language despite opposition by English scientists and the fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book
The Botanic GardenThe Botanic Garden is a set of two poems, The Economy of Vegetation and The Loves of the Plants, by the British poet and naturalist Erasmus Darwin. The Economy of Vegetation celebrates technological innovation, scientific discovery and offers theories concerning contemporary scientific questions,...
(1791) by
Erasmus DarwinErasmus Darwin was an English physician who turned down the invitation of George III for him to be a Royal Physician. He was also a natural philosopher, physiologist, abolitionist, inventor and poet...
, grandfather of
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
.
Later history
John DaltonJohn Dalton FRS was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness .-Early life:John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth in Cumberland,...
's original atomic hypothesis assumed that all elements were monoatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, giving the
atomic massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
of oxygen as 8 times that of hydrogen, instead of the modern value of about 16. In 1805,
Joseph Louis Gay-LussacJoseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries.- Biography :Gay-Lussac was born at...
and
Alexander von Humboldtwas a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher, and linguist, Wilhelm von Humboldt...
showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811
Amedeo AvogadroLorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto, Count of Quaregna and Cerreto was an Italian savant. He is most noted for his contributions to molecular theory, including what is known as Avogadro's law...
had arrived at the correct interpretation of water's composition, based on what is now called
Avogadro's lawAvogadro's law is a gas law named after Amedeo Avogadro who, in 1811, hypothesized that "Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of particles, or molecules." Thus, the number of molecules in a specific volume of gas is independent of...
and the assumption of diatomic elemental molecules.
By the late 19th century scientists realized that air could be liquefied, and its components isolated, by compressing and cooling it. Using a
cascadeIn chemical engineering, a cascade is a plant consisting of several similar stages with each processing the output from the previous stage. Cascades are most commonly used in isotope separation, distillation and other separation or purification processes....
method, Swiss chemist and physicist
Raoul Pierre PictetRaoul-Pierre Pictet was a Swiss physicist and the first person to liquefy nitrogen. He was born in Geneva and served as professor in the university of that city...
evaporatedEvaporation is the vaporization of a liquid and the reverse, of condensation. A type of phase transition, it is the process by which molecules in a liquid state spontaneously become gaseous . Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed...
liquid
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877 to the
French Academy of SciencesThe French Academy of Sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research...
in Paris announcing his discovery of
liquid oxygenLiquid oxygen is a form of the element oxygen. It has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horse shoe magnet...
. Just two days later, French physicist
Louis Paul CailletetLouis-Paul Cailletet was a French physicist and inventor.- Life and work :Cailletet was born in Châtillon-sur-Seine, Côte-d'Or. Educated in Paris, Cailletet returned to Chatillon to manage his father's ironworks...
announced his own method of liquefying molecular oxygen. Only a few drops of the liquid were produced in either case so no meaningful analysis could be conducted. Oxygen was liquified in stable state for the first time on March 29, 1877 by Polish scientists from
Jagiellonian UniversityThe Jagiellonian University was established in 1364 by Casimir III the Great in Kraków...
, Zygmunt Wróblewski and
Karol OlszewskiKarol Stanisław Olszewski was a Polish chemist, mathematician and physicist.-Life:...
.
In 1891 Scottish chemist
James DewarSir James Dewar FRS was a British chemist and physicist. He is probably best-known today for his invention of the Dewar flask, which he used in conjunction with extensive research into the liquefaction of gases...
was able to produce enough liquid oxygen to study. The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer
Carl von LindeProfessor Doctor Carl Paul Gottfried von Linde was a German engineer who developed refrigeration and gas separation technologies...
and British engineer William Hampson. Both men lowered the temperature of air until it liquefied and then
distilledDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
the component gases by boiling them off one at a time and capturing them. Later, in 1901, oxyacetylene
weldingWelding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
was demonstrated for the first time by burning a mixture of
acetyleneAcetylene is the chemical compound with the formula HC
2H. It is a hydrocarbon and the simplest alkyne. This colourless gas is widely used as a fuel and a chemical building block...
and compressed . This method of welding and cutting metal later became common.
In 1923 the American scientist
Robert H. GoddardRobert Hutchings Goddard , U.S. professor of physics and scientist, was a pioneer of controlled, liquid-fueled rocketry. He launched the world's first liquid-fueled rocket on March 16, 1926. From 1930 to 1935, he launched rockets that attained speeds of up to 885 km/h...
became the first person to develop a
rocket engineA rocket engine or simply "rocket" is a jet engine[Rocket Propulsion Elements; 7th edition- chapter 1] that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
; the engine used
gasolineGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines...
for fuel and liquid oxygen as the oxidizer. Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926 in
Auburn, MassachusettsAuburn is a town in Worcester County, Massachusetts, United States. The population was 15,901 at the 2000 census.- History :Auburn was first settled in 1714 and was officially incorporated in 1778 as the town of Ward, in honor of American Revolution General Artemas Ward...
, USA.
Industrial production
Two major methods are employed to produce 100 million tonnes of extracted from air for industrial uses annually. The most common method is to
fractionally distillFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
liquefied air into its various components, with nitrogen
distillingDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
as a vapor while oxygen is left as a liquid.
The other major method of producing gas involves passing a stream of clean, dry air through one bed of a pair of identical
zeoliteZeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
molecular sieves, which absorbs the nitrogen and delivers a gas stream that is 90% to 93% . Simultaneously, nitrogen gas is released from the other nitrogen-saturated zeolite bed, by reducing the chamber operating pressure and diverting part of the oxygen gas from the producer bed through it, in the reverse direction of flow. After a set cycle time the operation of the two beds is interchanged, thereby allowing for a continuous supply of gaseous oxygen to be pumped through a pipeline. This is known as
pressure swing adsorptionPressure Swing Adsorption is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation...
. Oxygen gas is increasingly obtained by these non-
cryogenicIn physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. Rather than the familiar temperature scales of Fahrenheit and Celsius, cryogenicists use the Kelvin scales...
technologies (see also the related
vacuum swing adsorptionVacuum swing adsorption is a non-cryogenic gas separation technology.Using special solids, or absorbents, VSA segregates certain gases from a gaseous mixture under minimal pressure according to the species' molecular characteristics and affinity for the absorbents...
).
Oxygen gas can also be produced through
electrolysis of waterElectrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water...
into molecular oxygen and hydrogen. DC electricity must be used: if AC is used, the gases in each limb consist of hydrogen and oxygen in the explosive ratio 2:1. Contrary to popular belief, the 2:1 ratio observed in the DC electrolysis of acidified water does not prove that the empirical formula of water is H2O unless certain assumptions are made about the molecular formulae of hydrogen and oxygen themselves.
A similar method is the electrocatalytic evolution from oxides and
oxoacidAn oxoacid is an acid which contains oxygen. More specifically, it is an acid which:#contains oxygen;#contains at least one other element;#has at least one hydrogen atom bound to oxygen; and#forms an ion by the loss of one or more protons....
s. Chemical catalysts can be used as well, such as in
chemical oxygen generatorA chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
s or oxygen candles that are used as part of the life-support equipment on submarines, and are still part of standard equipment on commercial airliners in case of depressurization emergencies. Another air separation technology involves forcing air to dissolve through
ceramicA ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
membranes based on
zirconium dioxideZirconium dioxide , sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral, baddeleyite...
by either high pressure or an electric current, to produce nearly pure gas.
In large quantities, the price of liquid oxygen in 2001 was approximately $0.21/kg. Since the primary cost of production is the energy cost of liquefying the air, the production cost will change as energy cost varies.
For reasons of economy, oxygen is often transported in bulk as a liquid in specially insulated tankers, since one
litreThe litre or liter is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case . The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau...
of liquefied oxygen is equivalent to 840 liters of gaseous oxygen at atmospheric pressure and 20 °
CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
. Such tankers are used to refill bulk liquid oxygen storage containers, which stand outside hospitals and other institutions with a need for large volumes of pure oxygen gas. Liquid oxygen is passed through
heat exchangerA heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
s, which convert the cryogenic liquid into gas before it enters the building. Oxygen is also stored and shipped in smaller
cylindersAn oxygen tank is a storage vessel for oxygen, which is either held under pressure in gas cylinders or as liquid oxygen in a cryogenic storage tank.Oxygen tanks are used to store gas for:* industrial processes including the manufacture of steel and methanol...
containing the compressed gas; a form that is useful in certain portable medical applications and
oxy-fuel welding and cuttingOxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively...
.
Medical
Uptake of from the air is the essential purpose of
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
, so oxygen supplementation is used in
medicineMedicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
.
Oxygen therapyOxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
is used to treat
emphysemaEmphysema is a lung disease, characterized by an abnormal, permanent enlargement of air spaces distal to the terminal bronchioles. The disease is coupled with the destruction of walls, but without obvious fibrosis...
,
pneumoniaPneumonia is an inflammatory illness of the lung. Frequently, it is described as lung parenchyma/alveolar inflammation and abnormal alveolar filling with fluid ....
, some heart disorders, and any
diseaseA disease or medical condition isan abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs...
that impairs the body's ability to take up and use gaseous oxygen. Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices.
Oxygen tentthumb|300pxAn oxygen tent consists in a canopy placed over the head and shoulders or over the entire body of a patient to provide oxygen at a higher level than normal.-External links:*...
s were once commonly used in oxygen supplementation, but have since been replaced mostly by the use of
oxygen maskAn oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...
s or
nasal cannulaThe nasal cannula is a device used to deliver supplemental oxygen to a patient or person in need of extra oxygen. This device consists of a plastic tube which fits behind the ears, and a set of two prongs which are placed in the nostrils. Oxygen flows from these prongs...
s.
Hyperbaric (high-pressure) medicine uses special oxygen chambers to increase the
partial pressureIn a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of around the patient and, when needed, the medical staff.
Carbon monoxide poisoningCarbon monoxide poisoning occurs after enough inhalation of carbon monoxide . Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and non-irritating, it is very difficult for people to detect...
,
gas gangreneGas gangrene is a bacterial infection that produces gas within tissues in gangrene. It is a deadly form of gangrene usually caused by Clostridium bacteria. It is a medical emergency.-Features:...
, and
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
(the 'bends') are sometimes treated using these devices. Increased concentration in the lungs helps to displace
carbon monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
from the heme group of
hemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
. Oxygen gas is poisonous to the anaerobic bacteria that cause gas gangrene, so increasing its partial pressure helps kill them. Decompression sickness occurs in divers who decompress too quickly after a dive, resulting in bubbles of inert gas, mostly nitrogen and helium, forming in their blood. Increasing the pressure of as soon as possible is part of the treatment.
Oxygen is also used medically for patients who require
mechanical ventilationIn medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing.This may involve a machine called a ventilator or the breathing may be assisted by a physician or other suitable person compressing a bag or set of bellows...
, often at concentrations above 21% found in ambient air.
Life support and recreational use
A notable application of as a low-pressure
breathing gasBreathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
is in modern
space suitA space suit is a complex system of garments, equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space...
s, which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressure of . This trade-off of higher oxygen concentration for lower pressure is needed to maintain flexible spacesuits.
Scuba diverScuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons.Unlike early diving, which relied exclusively on air pumped from the surface, scuba...
s and
submarineA submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has only limited underwater capability...
rs also rely on artificially delivered , but most often use normal pressure, and/or mixtures of oxygen and air. Pure or nearly pure use in diving at higher-than-sea-level pressures is usually limited to rebreather, decompression, or emergency treatment use at relatively shallow depths (~6 meters depth, or less). Deeper diving requires significant dilution of with other gases, such as nitrogen or helium, to help prevent
oxygen toxicityOxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
.
People who climb mountains or fly in non-pressurized
fixed-wing aircraftA fixed-wing aircraft, usually called an airplane, aeroplane or plane, is an aircraft capable of flight using forward motion that causes air to pass over its wings to generate lift. Planes include jet engine and propeller driven vehicles propelled forward by thrust, as well as unpowered aircraft...
sometimes have supplemental supplies. Passengers traveling in (pressurized) commercial airplanes have an emergency supply of automatically supplied to them in case of cabin depressurization. Sudden cabin pressure loss activates
chemical oxygen generatorA chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
s above each seat, causing
oxygen maskAn oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...
s to drop and forcing iron filings into the
sodium chlorateSodium chlorate is a chemical compound with the chemical formula . When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic...
inside the canister. A steady stream of oxygen gas is produced by the
exothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light , electricity , or sound. Its etymology stems from the Greek prefix ex- and the Greek word thermein...
reaction. However, even this may pose a danger if inappropriately triggered: a
ValuJet airplaneValuJet Flight 592 was a flight that crashed on May 11, 1996 en route from Miami International Airport in Miami, Florida, United States, to William B. Hartsfield Atlanta International Airport in Atlanta, Georgia...
crashed after use-date-expired canisters, which were being shipped in the cargo hold, activated and caused fire. The canisters were mis-labeled as
empty, and carried against
dangerous goodsDangerous goods, also called hazardous materials or HazMat , are solids, liquids, or gases that can harm people, other living organisms, property, or the environment. They are often subject to chemical regulations...
regulations.
Oxygen, as a supposed mild
euphoricEuphoria is medically recognized as a mental/emotional state defined as a sense of great elation and wellbeing. Technically, euphoria is an affect, but the term is often colloquially used to define emotion as an intense state of transcendent happiness combined with an overwhelming sense of wellbeing...
, has a history of recreational use in
oxygen barAn oxygen bar is an establishment, or part of one, that sells oxygen for recreational use. Individual flavored scents may be added to enhance the experience...
s and in
sportSport is an activity that is governed by a set of rules or customs and often engaged in competitively. Sports commonly refer to activities where the physical capabilities of the competitor are the sole or primary determinant of the outcome , but the term is also used to include activities such as...
s. Oxygen bars are establishments, found in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
,
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
, and
Las Vegas, NevadaLas Vegas is the most populous city in the U.S. state of Nevada, the seat of Clark County, and an internationally renowned major resort city for gambling, shopping, fine dining, and entertainment. Las Vegas, which bills itself as The Entertainment Capital of the World, is famous for the number of...
since the late 1990s that offer higher than normal exposure for a fee. Professional athletes, especially in
American footballAmerican football, known in the United States and Canada simply as football, and often as Gridiron or Tackle football outside North America, is a competitive team sport known for combining strategy with physical play. The objective of the game is to score points by advancing the ball into the...
, also sometimes go off field between plays to wear oxygen masks in order to get a supposed "boost" in performance. However, the reality of a pharmacological effect is doubtful; a
placeboA placebo is a sham medical intervention. In one common placebo procedure, a patient is given an inert sugar pill, told that it may improve his/her condition, but not told that it is in fact inert...
or psychological boost being the most plausible explanation. Available studies support a performance boost from enriched mixtures only if they are breathed
during actual aerobic exercise. Other recreational uses include pyrotechnic applications, such as George Goble's five-second ignition of
barbecueBarbecue or barbeque is a method and apparatus for cooking meat, with the heat and hot gases of a fire, smoking wood, or hot coals of charcoal or a propane gas grill, and may...
grills.
Industrial
SmeltingSmelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
of
iron oreIron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of magnetite , hematite , goethite, limonite or...
into
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
consumes 55% of commercially produced oxygen. In this process, is injected through a high-pressure lance into molten iron, which removes
sulfurSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
impurities and excess
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
as the respective oxides, and . The reactions are
exothermicAn exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
, so the temperature increases to 1,700 °
CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
.
Another 25% of commercially produced oxygen is used by the chemical industry.
EthyleneEthylene is the chemical compound with the formula C
2H
4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin. It is extremely important in industry and also has a role in biology as a hormone...
is reacted with to create
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
, which, in turn, is converted into
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
; the primary feeder material used to manufacture a host of products, including
antifreezeAntifreeze is a cryoprotectant used in internal combustion engines, and for many other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from undergoing physical stresses and catastrophic deformation due to the...
and
polyesterPolyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
polymers (the precursors of many
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
s and
fabricA fabric is a textile material, and is short for "textile fabrication".Fabric may also refer to:*Fabric , the spatial and geometric configuration of elements within a rock*fabric , a nightclub in London, EnglandIn computing:...
s).
Most of the remaining 20% of commercially produced oxygen is used in medical applications, metal cutting and welding, as an oxidizer in rocket fuel, and in
water treatmentWater treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...
. Oxygen is used in oxyacetylene welding burning
acetyleneAcetylene is the chemical compound with the formula HC
2H. It is a hydrocarbon and the simplest alkyne. This colourless gas is widely used as a fuel and a chemical building block...
with to produce a very hot flame. In this process, metal up to 60
cmA centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the current SI base unit of length. Centi is the SI prefix for a factor of...
thick is first heated with a small oxy-acetylene flame and then quickly cut by a large stream of . Rocket propulsion requires a fuel and an oxidizer. Larger
rocketA rocket or rocket vehicle is a missile, spacecraft, aircraft or other vehicle which obtains thrust by the reaction of the rocket to the ejection of a jet of fast moving fluid exhaust from a rocket engine. Chemical rockets create their exhaust by the combustion of rocket propellant...
s use liquid oxygen as their oxidizer, which is mixed and ignited with the fuel for propulsion.
Scientific
PaleoclimatologistsPaleoclimatology is the study of climate change taken on the scale of the entire history of Earth. It uses records from ice sheets, tree rings, sediment, and rocks to determine the past state of the climate system on Earth....
measure the ratio of
oxygen-18Oxygen-18 is a natural, stable isotope of oxygen and one of the environmental isotopes.18O is an important precursor for the production of fluorodeoxyglucose used in positron emission tomography...
and oxygen-16 in the shells and
skeletonIn biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa. Exoskeletons are external, as is typical of many invertebrates; they enclose the soft tissues and organs of the...
s of marine organisms to determine what the climate was like millions of years ago (see
oxygen isotope ratio cycleOxygen isotope ratio cycles are cyclical variations in the ratio of the mass of oxygen with an atomic weight of 18 to the mass of oxygen with an atomic weight of 16 present in some substance, such as polar ice or calcite in ocean core samples. The ratio is linked to water temperature of ancient...
).
SeawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
molecules that contain the lighter
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
, oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18; this disparity increases at lower temperatures. During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and the seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate. Paleoclimatologists also directly measure this ratio in the water molecules of
ice coreAn ice core is a core sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods...
samples that are up to several hundreds of thousands of years old.
Planetary geologistsThe geology of solar terrestrial planets mainly deals with the geological aspects of four planets of the Solar system namely, Mercury, Venus, Earth, and Mars and one terrestrial dwarf planet, Ceres. Objects like Pluto are similar to terrestrial planets in the fact that they do have a solid surface,...
have measured different abundances of oxygen isotopes in samples from the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
, the
MoonThe Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is , about thirty times the diameter of the Earth. The common centre of mass of the system is located at about —a quarter the Earth's...
,
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
, and
meteoriteA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s, but were long unable to obtain reference values for the isotope ratios in the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
, believed to be the same as those of the primordial solar nebula. However, analysis of a
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
wafer exposed to the
solar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...
in space and returned by the crashed
Genesis spacecraftThe Genesis spacecraft collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA "sample return mission" to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon...
has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from the Sun's
disk of protoplanetary materialA protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star or Herbig star...
prior to the coalescence of dust grains that formed the Earth.
Oxygen presents two spectrophotometric
absorption bandAn absorption band is a range of wavelengths in the electromagnetic spectrum which are able to excite a particular transition in a substance. See absorption spectrum...
s peaking at the wavelengths 687 and 760
nmA nanometre is a unit of length in the metric system, equal to one billionth of a meter....
. Some
remote sensingRemote sensing is the small or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device that are wireless, or not in physical or intimate contact with the object...
scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a
satelliteEarth observation satellites are satellites specifically designed to observe Earth from orbit, similar toreconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. Geostationary satellites hover over the same spot, providing...
platform. This approach exploits the fact that in those bands it is possible to discriminate the vegetation's reflectance from its
fluorescenceFluorescence is the emission of visible light by a substance that has absorbed light of a differing, usually invisible, wavelength. Absorption of a photon triggers the emission of a photon with a longer wavelength. A shorter wavelength emission is sometimes observed from multiple photon absorption...
, which is much weaker. The measurement is technically difficult owing to the low
signal-to-noise ratioSignal-to-noise ratio is an electrical engineering measurement, also used in other fields , defined as the ratio of a signal power to the noise power corrupting the signal...
and the physical structure of vegetation; but it has been proposed as a possible method of monitoring the
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
from satellites on a global scale.
Compounds
The
oxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as
peroxideA peroxide is a compound containing an oxygen-oxygen single bond. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately.- Organic chemistry :...
s. Compounds containing oxygen in other oxidation states are very uncommon: −1/2 (
superoxideSuperoxide is an anion with the chemical formula O
2−. It is important as the product of the one-electron reduction of dioxygen O
2, which occurs widely in nature...
s), −1/3 (
ozonideOzonide is an unstable, reactive polyatomic anion O
3−, derived from ozone, or an organic compound similar to organic peroxide formed by a reaction of ozone with an unsaturated compound.-Inorganic ozonides:...
s), 0 (
elementalThere are several known allotropes of oxygen:*Free radicals O1 - unstable*dioxygen, O2 - colorless*ozone, O3 - blue*tetraoxygen, O4 - metastable...
,
hypofluorous acidHypofluorous acid is the chemical compound with the formula HFO. It is an intermediate in the oxidation of water by fluorine, which produces hydrogen fluoride and oxygen. It is the only hypohalic acid that can be isolated as a solid. HOF is explosive, decomposing to oxygen and HF...
), +1/2 (
dioxygenylThe dioxygenyl ion, , is a rarely-encountered oxycation in which both oxygen atoms have an oxidation state of +½. It is formally derived from oxygen by the removal of an electron:...
), +1 (
dioxygen difluorideDioxygen difluoride is a compound with the formula O
2F
2. This yellow compound is a strong oxidant and decomposes into OF
2 and oxygen even at −160 °C .-Preparation:...
), and +2 (
oxygen difluorideOxygen difluoride is the chemical compound with the formula OF2. As predicted by VSEPR theory, the molecule adopts a "V" shaped structure like H2O, but it has very different properties, being a strong oxidizer.-Preparation:...
).
Oxides and other inorganic compounds
WaterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
is the oxide of
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
and the most familiar oxygen compound. Hydrogen atoms are covalently bonded to oxygen in a water molecule but also have an additional attraction (about 23.3 kJ·mol
−1 per hydrogen atom) to an adjacent oxygen atom in a separate molecule. These
hydrogen bondA hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, like nitrogen, oxygen or fluorine . The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s between water molecules hold them approximately 15% closer than what would be expected in a simple liquid with just
Van der Waals forceIn physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules...
s.
Due to its
electronegativityElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
, oxygen forms
chemical bondA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
s with almost all other elements at elevated temperatures to give corresponding
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s. However, some elements readily form oxides at
standard conditions for temperature and pressureIn physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data...
; the
rustRust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances...
ing of
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
is an example. The surface of metals like
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
and
titaniumTitanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other...
are oxidized in the presence of air and become coated with a thin film of oxide that
passivatesPassivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and...
the metal and slows further
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. Some of the
transition metal oxidesTransition metal oxides comprise a class of materials that contain transition elements and oxygen. They include insulators as well as metals. Often the same material may display both types of transport properties, hence a Metal-Insulator transition, obtained by varying either temperature or...
are found in nature as
non-stoichiometric compoundNon-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and therefore violate the law of definite proportions. Often, they are solids that contain crystallographic point defects, such as interstitial...
s, with a slightly less metal than the
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
would show. For example, the natural occurring
FeOIron oxide, also known as ferrous oxide, iron oxide/oxidized iron or more commonly rusted iron, is one of the iron oxides. It is a black-colored powder with the chemical formula . It consists of the chemical element iron in the oxidation state of 2 bonded to oxygen. Its mineral form is known as...
(
wüstiteWüstite is a mineral form of iron oxide found with meteorites and native iron. It has a gray color with a greenish tint in reflected light. Wüstite crystallizes in the isometric - hexoctahedral crystal system in opaque to translucent metallic grains. It has a Mohs hardness of 5 to 5.5 and a...
) is actually written as , where
x is usually around 0.05.
Oxygen as a compound is present in the atmosphere in trace quantities in the form of
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
. The earth's crustal
rockIn geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
is composed in large part of oxides of
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
(
silicaThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of ' and has been known for its hardness since antiquity. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms...
, found in
graniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their...
and
sandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
),
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
(
aluminium oxideAluminium oxide is an amphoteric oxide of aluminium with the chemical formula
23. It is also commonly referred to as alumina, corundum, sapphire, ruby or aloxite in the mining, ceramic and materials science communities. It is produced by the Bayer process from bauxite...
, in
bauxiteBauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al
3, boehmite γ-AlO, and diaspore α-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO
2...
and
corundumCorundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present...
), iron (
iron(III) oxideIron oxide—also known as ferric oxide, ferric iron, hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust—is one of the several oxide compounds of iron, and has paramagnetic properties...
, in
hematiteHematite, also spelled as hæmatite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
and
rustRust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances...
) and other
metalA metal is a chemical element that is a good conductor of both electricity and heat, forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions...
s.
The rest of the Earth's crust is also made of oxygen compounds, in particular
calcium carbonateCalcium carbonate is a chemical compound with the chemical formula CaCO
3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural...
(in
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
) and
silicateA silicate is a compound containing an ion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2−, but the silicate species that are encountered most often...
s (in
feldsparFeldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
s). Water-
solubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure...
silicates in the form of , , and are used as
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s and
adhesiveAdhesive or glue is a compound in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry...
s.
Oxygen also acts as a ligand for transition metals, forming metal– bonds with the
iridiumIridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
atom in
Vaska's complexVaska's complex is the trivial name for the chemical compound trans-chlorocarbonylbisiridium, which has the formula IrCl[P3]2...
, with the
platinumPlatinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements...
in
{{otheruses4|the chemical element and its most stable form, {{chem|O|2}} or dioxygen|other forms of this element|Allotropes of oxygen|other uses|Oxygen (disambiguation)}}
{{pp-semi-vandalism|small=yes}}
Oxygen ({{pron-en|ˈɒksɨdʒɨn}}, {{respell|OK|si-jin}}, from the GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
roots ὀξύς (oxys) (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the
elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
with
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
8 and represented by the symbol
O. It is a member of the
chalcogenThe chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
group on the
periodic tableThe periodiс table of the chemical elements is a tabular display of the chemical elements...
, and is a highly reactive
nonmetalNonmetal, or non-metal, is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal...
lic
period 2 elementA period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical...
that readily forms
compoundsA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
(notably
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s) with almost all other elements. At standard temperature and pressure two atoms of the element
bindA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
to form dioxygen, a colorless, odorless, tasteless diatomic
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
with the formula {{chem|O|2}}. Oxygen is the
third most abundantThe abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. Abundance may be variously measured by the mass-fraction , or mole-fraction , or by volume fraction...
element in the universe by mass after
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
and
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
and the
most abundant-Earth bulk continental crust and upper continental crust:*C1 — Crust: CRC Handbook*C2 — Crust: Kaye & Laby*C3 — Crust: Greenwood*C4 — Crust: Ahrens *C5 — Crust: Ahrens...
element by mass in the Earth's crust. Diatomic oxygen gas constitutes 20.9% of the volume of
airThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
.
All major classes of structural molecules in living organisms, such as
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s,
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s, and
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s, contain oxygen, as do the major
inorganic compoundTraditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin...
s that comprise animal shells, teeth, and bone. Oxygen in the form of {{chem|O|2}} is produced from water by
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
,
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
and plants during
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
and is used in
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
for all complex life. Oxygen is toxic to
obligately anaerobic organismsObligate anaerobes are anaerobic organisms that fail to grow in the presence of oxygen.-Metabolism:Obligate anaerobes die in presence of oxygen due to the absence of the enzymes superoxide dismutase and catalase, which would convert the lethal superoxide formed in their cells due to the presence...
, which were the dominant form of
early lifeThe evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved. It stretches back over , possibly as far as , and evolution continues, even in humans. All present-day organisms use the same large set of complex chemical reactions, which indicates that...
on Earth until {{chem|O|2}} began to accumulate in the atmosphere 2.5 billion years ago. Another form (
allotropeThere are several known allotropes of oxygen:*Free radicals O1 - unstable*dioxygen, O2 - colorless*ozone, O3 - blue*tetraoxygen, O4 - metastable...
) of oxygen,
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
({{chem|O|3}}), helps protect the biosphere from ultraviolet radiation with the high-altitude
ozone layerThe ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here...
, but is a pollutant near the surface where it is a by-product of
smogSmog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide...
. At even higher
low earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
altitudes atomic oxygen is a significant presence and a cause of
erosion for spacecraftCorrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet light and x-rays, high-energy charged particles...
.
Oxygen was independently discovered by
Carl Wilhelm ScheeleCarl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
, in
UppsalaUppsala is the capital of Uppsala County and the fourth largest city of Sweden with 144,839 inhabitants....
, in 1773 or earlier, and
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
in
WiltshireWiltshire is a ceremonial county in the south west of England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers 3,485 km²...
, in 1774, but Priestley is often given priority because his publication came out in print first. The name
oxygen was coined in 1777 by
Antoine LavoisierAntoine-Laurent de Lavoisier ; ), the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology...
, whose experiments with oxygen helped to discredit the then-popular
phlogiston theoryThe phlogiston theory , first stated in 1667 by Johann Joachim Becher, is a defunct scientific theory that posited the existence of a fire-like element called "phlogiston" that was contained within combustible bodies, and released during combustion...
of
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. Oxygen is produced industrially by
fractional distillationFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
of liquefied air, use of
zeoliteZeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
s to remove
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
and
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
from air,
electrolysis of waterElectrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water...
and other means. Uses of oxygen include the production of steel, plastics and textiles;
rocket propellantRocket propellant is mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot...
;
oxygen therapyOxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
; and life support in aircraft, submarines,
spaceflightHuman spaceflight is spaceflight with a human crew and possibly passengers. This makes it unlike robotic space probes or remotely-controlled satellites...
and
divingUnderwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
.
Structure
At standard temperature and pressure, oxygen is a colorless, odorless gas with the
molecularA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
formula {{chem|O|2}}, in which the two oxygen atoms are
chemically bondedA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
to each other with a spin triplet
electron configurationIn atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
. This bond has a
bond orderBond order is the number of chemical bonds between a pair of atoms. For example, in diatomic nitrogen N≡N the bond order is 3, while in acetylene H−C≡C−H the bond order between the two carbon atoms is also 3, and the C−H bond order is 1. Bond order gives an indication to the stability of a bond. In...
of two, and is often simplified in description as a
double bondA double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
or as a combination of one two-electron bond and two three-electron bonds.
Triplet oxygenTriplet oxygen is the ground state of the oxygen molecule. The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals...
(not to be confused with
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
, {{chem|O|3}}) is the ground state of the {{chem|O|2}} molecule. The electron configuration of the molecule has two unpaired electrons occupying two
degenerateDegenerate orbitals for electrons in an atomic subshell are orbitals at identical energy levels. These are important in physical chemistry because they affect the ways electrons fill atoms . For example, all the 3p orbitals have same energy level, and so do all the 5d orbitals. Each orbital is...
molecular orbitalIn chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The use of the term...
s. These orbitals are classified as
antibondingAntibonding is a type of chemical bonding. An antibonding orbital is a form of molecular orbital that is located outside the region of two distinct nuclei. The overlap of the constituent atomic orbitals is said to be 'out of phase' and as such the electrons present in each antibonding orbital are...
(weakening the bond order from three to two), so the diatomic oxygen bond is weaker than the diatomic
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
triple bond in which all bonding molecular orbitals are filled, but some antibonding orbitals are not.
In normal triplet form, {{chem|O|2}} molecules are
paramagneticParamagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability of ≥1 .The magnetic moment induced by the applied field is linear in the field...
—they form a magnet in the presence of a magnetic field—because of the
spinIn particle physics and quantum mechanics, spin is a fundamental characteristic property of elementary particles including the force carriers , composite particles , and atomic nuclei....
magnetic momentThe magnetic moment of a system is a measure of the strength and the direction of its magnetism. More technically , the term magnetic moment of a system usually refers to its magnetic dipole moment, and quantifies the contribution...
s of the unpaired electrons in the molecule, and the negative exchange energy between neighboring {{chem|O|2}} molecules. Liquid oxygen is attracted to a
magnetA magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets.A permanent magnet is an object made from a...
to a sufficient extent that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet.
Singlet oxygenSinglet oxygen is the common name used for the diamagnetic form of molecular oxygen , which is less stable than the normal triplet oxygen. Because of its unusual properties, singlet oxygen can persist for over an hour at room temperature, depending on the environment...
, a name given to several higher-energy species of molecular {{chem|O|2}} in which all the electron spins are paired, is much more reactive towards common
organic moleculesAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the
troposphereThe troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor and aerosols....
by the photolysis of ozone by light of short wavelength, and by the immune system as a source of active oxygen.
CarotenoidCarotenoids are organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria....
s in photosynthetic organisms (and possibly also in animals) play a major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues.
Allotropes
{{main|Allotropes of oxygen}}
The common
allotropeAllotropy or allotropism is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner...
of elemental oxygen on Earth is called dioxygen, {{chem|O|2}}. It has a bond length of 121
pmA picometre is a unit of length in the metric system, equal to one trillionth or one billionth , i.e. of a meter, which is the current SI base unit of length...
and a bond energy of 498
kJ·mol-1The joule per mole is an SI derived unit of energy per amount of material. Energy is measured in joules, and the amount of material is measured in moles....
. This is the form that is used by complex forms of life, such as animals, in cellular respiration (see Biological role) and is the form that is a major part of the Earth's atmosphere (see Occurrence). Other aspects of {{chem|O|2}} are covered in the remainder of this article.
Trioxygen ({{chem|O|3}}) is usually known as
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
and is a very reactive allotrope of oxygen that is damaging to lung tissue. Ozone is produced in the upper atmosphere when {{chem|O|2}} combines with atomic oxygen made by the splitting of {{chem|O|2}} by
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(UV) radiation. Since ozone absorbs strongly in the UV region of the
spectrumThe electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, the
ozone layerThe ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here...
of the upper atmosphere functions as a protective radiation shield for the planet. Near the Earth's surface, however, it is a
pollutantAir pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment, into the atmosphere....
formed as a by-product of automobile exhaust. The metastable molecule
tetraoxygenThe tetraoxygen molecule , also called oxozone was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxygen to obey Curie's law...
({{chem|O|4}}) was discovered in 2001, and was assumed to exist in one of the six phases of
solid oxygenSolid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K . Solid oxygen O
2, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red .Oxygen molecules have attracted attention because of the...
. It was proven in 2006 that this phase, created by pressurizing {{chem|O|2}} to 20
GPaThe pascal is the SI derived unit of pressure, stress, Young's modulus and tensile strength. It is a measure of force per unit area, defined as one newton per square metre...
, is in fact a rhombohedral {{chem|O|8}}
clusterIn chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
. This cluster has the potential to be a much more powerful
oxidizerAn oxidizing agent can be defined as either:#a chemical compound that readily transfers oxygen atoms, or#a substance that gains electrons in a redox chemical reaction...
than either {{chem|O|2}} or {{chem|O|3}} and may therefore be used in rocket fuel. A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa and it was shown in 1998 that at very low temperatures, this phase becomes
superconductingSuperconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field . It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral...
.
Physical properties
{{seealso|Liquid oxygen|solid oxygen}}
Oxygen is more
solubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure...
in water than nitrogen; water contains approximately 1 molecule of {{chem|O|2}} for every 2 molecules of {{chem|N|2}}, compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L
−1) dissolves at 0 °C than at 20 °C (7.6 mg·L
−1). At 25 °C and {{convert|1|atm|lk=on|sigfig=4}} of air, freshwater contains about 6.04
milliliterThe litre or liter is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case . The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau...
s (mL) of oxygen per
liter
, whereas
seawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
contains about 4.95 mL per liter. At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for water and 7.2 mL (45% more) per liter for sea water.
Oxygen condenses at 90.20
KThe kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero kelvin...
(−182.95 °C, −297.31 °F), and freezes at 54.36 K (−218.79 °C, −361.82 °F). Both
liquidLiquid oxygen is a form of the element oxygen. It has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horse shoe magnet...
and
solidSolid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K . Solid oxygen O
2, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red .Oxygen molecules have attracted attention because of the...
{{chem|O|2}} are clear substances with a light
sky-blueDiffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. It is also called skylight, diffuse skylight, or sky radiation and is the reason for changes in the colour of the sky...
color caused by absorption in the red (in contrast with the blue color of the sky, which is due to
Rayleigh scatteringRayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light, which may be individual atoms or molecules. It can occur when light travels in transparent solids and liquids, but is most prominently seen in gases...
of blue light). High-purity liquid {{chem|O|2}} is usually obtained by the
fractional distillationFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
of liquefied air; Liquid oxygen may also be produced by condensation out of air, using liquid nitrogen as a coolant. It is a highly reactive substance and must be segregated from combustible materials.
Isotopes and stellar origin
{{main|Isotopes of oxygen}}
Naturally occurring oxygen is composed of three stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s,
16O,
17O, and
18OOxygen-18 is a natural, stable isotope of oxygen and one of the environmental isotopes.18O is an important precursor for the production of fluorodeoxyglucose used in positron emission tomography...
, with
16O being the most abundant (99.762%
natural abundanceIn chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass of these isotopes is the atomic weight listed for the element in the periodic table...
).
Most
16O is
synthesizedNucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons . It is thought that the primordial nucleons themselves were formed from the quark-gluon plasma from the Big Bang as it cooled below two trillion degrees...
at the end of the
helium fusionHelium fusion is a kind of nuclear fusion, with the nuclei involved being helium.The fusion of helium-4 nuclei is known as the triple-alpha process, because fusion of just two helium nuclei only produces beryllium-8, which is unstable and breaks back down to two helium nuclei with a half life of...
process in
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
s but some is made in the
neon burning processThe neon burning process is a set of nuclear fusion reactions that take place in massive stars . Neon burning requires high temperatures and densities ....
.
17O is primarily made by the burning of hydrogen into
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
during the
CNO cycleThe CNO cycle , or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain. Theoretical models show that the CNO cycle is the dominant source of energy in stars heavier than about 1.5 times the mass...
, making it a common isotope in the hydrogen burning zones of stars. Most
18O is produced when
14NNitrogen-14 is a stable, non-radioactive isotope of the chemical element nitrogen.Nitrogen-14 comprises approximately 99% of all naturally formed nitrogen. It is the source of naturally-occurring carbon-14, which is created when cosmic radiation interacts with nitrogen-14 in the upper atmosphere. ...
(made abundant from CNO burning) captures a
4HeHelium-4 is a non-radioactive and light isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. The total spin of...
nucleus, making
18O common in the helium-rich zones of stars.
Fourteen radioisotopes have been characterized, the most stable being
15O with a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of 122.24 seconds (s) and
14O with a half-life of 70.606 s. All of the remaining
radioactiveRadioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter...
isotopes have half-lives that are less than 27 s and the majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than
16O is
β+ decayPositron emission is a type of beta decay, sometimes referred to as "beta plus" . In beta plus decay, a proton is converted, via the weak force, to a neutron, a positron , and a neutrino.Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40,...
to yield nitrogen, and the most common mode for the isotopes heavier than
18O is
beta decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
to yield
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
.
Occurrence
{{seealso|Silicate minerals|Category:Oxide minerals}}
Oxygen is the most abundant chemical element, by mass, in our biosphere, air, sea and land.
Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. About 0.9% of the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
's mass is oxygen. Oxygen constitutes 49.2% of the Earth's crust by mass and is the major component of the world's oceans (88.8% by mass). Oxygen gas is the second most common component of the
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, taking up 21.0% of its volume and 23.1% of its mass (some 10
15 tonnes). Earth is unusual among the planets of the
Solar SystemThe Solar System consists of the Sun and those celestial objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago...
in having such a high concentration of oxygen gas in its atmosphere:
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
(with 0.1% {{chem|O|2}} by volume) and
VenusVenus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6...
have far lower concentrations. However, the {{chem|O|2}} surrounding these other planets is produced solely by ultraviolet radiation impacting oxygen-containing molecules such as carbon dioxide.
The unusually high concentration of oxygen gas on Earth is the result of the
oxygen cycleThe oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere , the biosphere , and the lithosphere...
. This
biogeochemical cycleIn ecology and Earth science, a biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth...
describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, the
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
, and the
lithosphereThe lithosphere is the rigid outermost shell of a rocky planet.- Earth's lithosphere :...
. The main driving factor of the oxygen cycle is
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
, which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while
respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
and
decayDecomposition is the process by which tissues of a dead organism break down into simpler forms of matter. The process is essential for new growth and development of living organisms because it recycles the finite matter that occupies physical space in the biome. Bodies of living organisms begin to...
remove it from the atmosphere. In the present equilibrium, production and consumption occur at the same rate of roughly 1/2000th of the entire atmospheric oxygen per year.
Free oxygen also occurs in solution in the world's water bodies. The increased solubility of {{chem|O|2}} at lower temperatures (see Physical properties) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content.
Polluted waterWater pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater. All water pollution affects organisms and plants that live in these water bodies and in almost all cases the effect is damaging either to individual species and populations but also to the natural...
may have reduced amounts of {{chem|O|2}} in it, depleted by decaying algae and other biomaterials (see
eutrophicationEutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem...
). Scientists assess this aspect of water quality by measuring the water's
biochemical oxygen demandBiochemical oxygen demand or BOD is a chemical procedure for determining the rate of uptake of dissolved oxygen by the rate biological organisms in a body of water use up oxygen. It is not a precise quantitative test, although it is widely used as an indication of the quality of water.BOD can be...
, or the amount of {{chem|O|2}} needed to restore it to a normal concentration.
Photosynthesis and respiration
In nature, free oxygen is produced by the light-driven splitting of water during oxygenic
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
.
Green algaeThe green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
and
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
in marine environments provide about 70% of the free oxygen produced on earth and the rest is produced by terrestrial plants.
A simplified overall formula for photosynthesis is:
-
- 6 {{CO2}} + 6 {{chem|H|2|O}} + photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s → {{chem|C|6|H|12|O|6}} + 6 {{chem|O|2}} (or simply carbon dioxide + water + sunlight → glucose + dioxygen)
Photolytic
oxygen evolutionOxygen evolution is the process of generating molecular oxygen through chemical reaction. Mechanisms of oxygen evolution include the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and...
occurs in the thylakoid membranes of photosynthetic organisms and requires the energy of four
photonIn physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s. Many steps are involved, but the result is the formation of a
protonThe proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H
+...
gradient across the thylakoid membrane, which is used to synthesize
ATPAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
via
photophosphorylationThe production of ATP using the energy of sunlight is called photophosphorylation. Only two sources of energy are available to living organisms: sunlight and oxidation-reduction reactions...
. The {{chem|O|2}} remaining after oxidation of the water molecule is released into the atmosphere.
Molecular dioxygen, {{chem|O|2}}, is essential for cellular respiration in all
aerobic organismAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. -Types:*Obligate aerobes require oxygen for aerobic cellular respiration...
s. Oxygen is used in
mitochondriaIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
to help generate
adenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
(ATP) during
oxidative phosphorylationOxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that...
. The reaction for aerobic respiration is essentially the reverse of photosynthesis and is simplified as:
-
- {{chem|C|6|H|12|O|6}} + 6 {{chem|O|2}} → 6 {{CO2}} + 6 {{chem|H|2|O}} + 2880 kJ·mol-1
In
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s, {{chem|O|2}} is
diffusedMolecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material...
through membranes in the lungs and into
red blood cellRed blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries. The cells are filled with hemoglobin, a...
s.
HemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
binds {{chem|O|2}}, changing its color from bluish red to bright red. Other animals use
hemocyaninHemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...
(
molluscMolluscs
[Spelled mollusk in the USA, see reasons given in Rosenberg's ; for the spelling "mollusc" see the reasons given by .] are animals belonging to the phylum Mollusca. There are around 93,000 recognized extant species, making it the largest marine phylum with about 23% of...
s and some
arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s) or
hemerythrinHemerythrin is an oligomeric protein responsible for oxygen transportation in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm, magelona. Recently, hemerythrin was discovered in methanotrophic bacterium Methylococcus capsulatus...
(
spiderSpiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s and
lobsterClawed lobsters compose a family of large marine crustaceans. Lobsters are economically important as seafood, forming the basis of a global industry that nets US$31.8 billion in trade annually....
s). A liter of blood can dissolve 200 cm
3 of {{chem|O|2}}.
Reactive oxygen speciesReactive oxygen species are free radicals that contain the oxygen atom. They are very small molecules that include oxygen ions and peroxides and can be either inorganic or organic. They are highly reactive due to the presence of unpaired valence shell electrons.ROS form as a natural byproduct of...
, such as
superoxideSuperoxide is an anion with the chemical formula O
2−. It is important as the product of the one-electron reduction of dioxygen O
2, which occurs widely in nature...
ion ({{chem|O|2|-}}) and
hydrogen peroxideHydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...
({{chem|H|2|O|2}}), are dangerous by-products of oxygen use in organisms. Parts of the
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
of higher organisms, however, create peroxide, superoxide, and singlet oxygen to destroy invading microbes. Reactive oxygen species also play an important role in the
hypersensitive responseThe hypersensitive response is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens. The HR is characterized by the rapid death of cells in the local region surrounding an infection. The HR serves to restrict the growth and spread of pathogens to other parts of...
of plants against pathogen attack.
An adult human in rest
inhalesBreathing is the process that takes oxygen in and carbon dioxide out of the body. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose...
1.8 to 2.4 grams of oxygen per minute. This amounts to more than 6 billion tonnes of oxygen inhaled by humanity per year.
Build-up in the atmosphere
{{Main|Geological history of oxygen|Biological role of oxygen}}
Free oxygen gas was almost nonexistent in
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
before photosynthetic
archaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . They have no cell nucleus or any other organelles within their cells...
and
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
evolved. Free oxygen first appeared in significant quantities during the
PaleoproterozoicThe Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
era (between 2.5 and 1.6 billion years ago). At first, the oxygen combined with dissolved
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
in the oceans to form
banded iron formationBanded iron formations are a distinctive type of rock often found in primordial sedimentary rocks. The structures consist of repeated thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...
s. Free oxygen started to gas out of the oceans 2.7 billion years ago, reaching 10% of its present level around 1.7 billion years ago.
The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have driven most of the
anaerobic organismAn anaerobic organism or anaerobe is any organism that does not require oxygen for growth and may even die in its presence. There are three types: obligate anaerobes, which cannot use oxygen for growth and are even harmed by it; aerotolerant organisms, which cannot use oxygen for growth, but...
s then living to
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
during the
oxygen catastropheThe Great Oxidation Event was a major environmental change around associated with the appearance of free oxygen in the atmosphere....
about 2.4 billion years ago. However,
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
using {{chem|O|2}} enables
aerobic organismAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. -Types:*Obligate aerobes require oxygen for aerobic cellular respiration...
s to produce much more ATP than anaerobic organisms, helping the former to dominate Earth's
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
. Photosynthesis and cellular respiration of {{chem|O|2}} allowed for the evolution of
eukaryotic cellEukaryotic Cell is an academic journal published by the American Society for Microbiology. The title is commonly abbreviated EC and the ISSN is 1535-9778 for the print version, and 1535-9786 for the electronic version....
s and ultimately complex multicellular organisms such as plants and animals.
Since the beginning of the
CambrianThe Cambrian is the first geological period of the Paleozoic era, lasting from ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux...
era 540 million years ago, {{chem|O|2}} levels have fluctuated between 15% and 30% by volume. Towards the end of the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
era (about 300 million years ago) atmospheric {{chem|O|2}} levels reached a maximum of 35% by volume, which may have contributed to the large size of insects and amphibians at this time. Human activities, including the burning of 7 billion
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s of
fossil fuelFossil fuels or mineral fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s each year have had very little effect on the amount of free oxygen in the atmosphere. At the current rate of photosynthesis it would take about 2,000 years to regenerate the entire {{chem|O|2}} in the present atmosphere.
Early experiments
One of the first known experiments on the relationship between
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and air was conducted by the second century BCE
GreekAncient Greece is the civilisation belonging to the period of Greek history lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman conquest of Greece after the Battle of Corinth. It is generally considered to be the seminal culture which provided the...
writer on mechanics,
Philo of ByzantiumPhilo of Byzantium , also known as Philo Mechanicus, a Greek writer on mechanics, flourished during the latter half of the 2nd century B.C...
. In his work
Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck.
Philo incorrectly surmised that parts of the air in the vessel were converted into the
classical elementMany philosophies and worldviews have used a set of archetypal classical elements, most developed sets of the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based...
fireFire has been an important part of all cultures and religions, from pre-history to modern day, and was vital to the development of civilization. It has been regarded in many different fashions throughout history.-Greek and Roman Tradition:...
and thus were able to escape through pores in the glass. Many centuries later
Leonardo da VinciLeonardo di ser Piero da Vinci was an Italian polymath, scientist, mathematician, engineer, inventor, anatomist, painter, sculptor, architect, botanist, musician and writer....
built on Philo's work by observing that a portion of air is consumed during combustion and
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
.
In the late 17th century,
Robert BoyleRobert Boyle was a natural philosopher, chemist, physicist, inventor, and gentleman scientist, also noted for his writings in theology. He is best known for the formulation of Boyle's law...
proved that air is necessary for combustion. English chemist
John MayowJohn Mayow FRS was a chemist, physician, and physiologist who is remembered today for conducting early research into respiration and the nature of air...
refined this work by showing that fire requires only a part of air that he called
spiritus nitroaereus or just
nitroaereus.
In one experiment he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
and combustion.
Mayow observed that
antimonyAntimony is a chemical element with the symbol Sb and atomic number 51. A metalloid, antimony has four allotropic forms. The stable form of antimony is a blue-white metalloid. Yellow and black antimony are unstable non-metals...
increased in weight when heated, and inferred that the nitroaereus must have combined with it. He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work
Tractatus duo in the tract "De respiratione".
Phlogiston theory
{{main|Phlogiston theory}}
Robert HookeRobert Hooke, FRS was an English natural philosopher, architect and polymath who played an important role in the scientific revolution, through both experimental and theoretical work....
,
Ole BorchOle Borch was a Danish scientist, physician, grammarian, and poet, most famous today for being the teacher at the Vor Frue Skole in Copenhagen of Nicholas Steno. Borch had studied medicine at the University of Copenhagen and distinguished himself in the plague of 1654, when a third of...
,
Mikhail LomonosovMikhail Vasilyevich Lomonosov was a Russian polymath, scientist and writer, who made important contributions to literature, education, and science. Among his discoveries was the atmosphere of Venus. His spheres of science were natural science, chemistry, physics, mineralogy, history, art,...
, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as an element. This may have been in part due to the prevalence of the philosophy of
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
called the phlogiston theory, which was then the favored explanation of those processes.
Established in 1667 by the German alchemist
J. J. BecherJohann Joachim Becher , was a German physician, alchemist, precursor of chemistry, scholar and adventurer, best known for his development of the phlogiston theory and his advancement of Austrian cameralism....
, and modified by the chemist
Georg Ernst StahlGeorg Ernst Stahl , was a German chemist and physician.He was born at Ansbach. Having graduated in medicine at the University of Jena in 1683, he became court physician to Duke Johann Ernst of Sachsen Weimar in 1687...
by 1731,
phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or
calxCalx is a residual substance, sometimes in the form of a fine powder, that is left when a metal or mineral combusts or is calcinated due to heat.Calx, especially of a metal, is now known as an oxide...
.
Highly combustible materials that leave little
residueIn chemistry, residue refers to the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group....
, such as wood or coal, were thought to be made mostly of phlogiston; whereas non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. The fact that a substance like wood actually
gains overall weight in burning was hidden by the buoyancy of the gaseous combustion products. Indeed one of the first clues that the phlogiston theory was incorrect was that metals, too, gain weight in rusting (when they were supposedly losing phlogiston).
Discovery
Oxygen was first discovered by
SwedishSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
pharmacist
Carl Wilhelm ScheeleCarl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
. He had produced oxygen gas by heating mercuric oxide and various
nitrateIn inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates.-Chemical properties:...
s by about 1772. Scheele called the gas 'fire air' because it was the only known supporter of combustion. He wrote an account of this discovery in a manuscript he titled
Treatise on Air and Fire, which he sent to his publisher in 1775. However, that document was not published until 1777.
In the meantime, an experiment was conducted by the
BritishThe Kingdom of Great Britain, also known as the United Kingdom of Great Britain, was a sovereign state in northwest Europe, in existence from 1707 to 1801...
clergyman
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
on August 1, 1774 focused sunlight on
mercuric oxideMercury oxide, also called mercuric oxide or simply mercury oxide, has a formula of HgO and a formula weight of 216.6. It has a red or orange color. Mercury oxide is a solid at room temperature and pressure...
(HgO) inside a glass tube, which liberated a gas he named 'dephlogisticated air'. He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air" which was included in the second volume of his book titled
Experiments and Observations on Different Kinds of AirExperiments and Observations on Different Kinds of Air is a six-volume work published by eighteenth-century British polymath Joseph Priestley which reports a series of his experiments on "airs" or gases, most notably his discovery of oxygen gas .-Airs:While working as a companion for Lord...
. Because he published his findings first, Priestley is usually given priority in the discovery.
The noted French chemist
Antoine Laurent LavoisierAntoine-Laurent de Lavoisier ; ), the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology...
later claimed to have discovered the new substance independently. However, Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele also posted a letter to Lavoisier on September 30, 1774 that described his own discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of the letter was found in Scheele's belongings after his death).
Lavoisier's contribution
What Lavoisier did indisputably do (although this was disputed at the time) was to conduct the first adequate quantitative experiments on oxidation and give the first correct explanation of how combustion works. He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
.
In one experiment, Lavoisier observed that there was no overall increase in weight when
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4...
and air were heated in a closed container. He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book
Sur la combustion en général, which was published in 1777. In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and
azote (Gk.
{{Polytonic|ἄζωτον}} "lifeless"), which did not support either.
Azote later became
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
in English, although it has kept the name in French and several other European languages.
Lavoisier renamed 'vital air' to
oxygène in 1777 from the
GreekAncient Greek is the historical stage in the development of the Greek language spanning across the Archaic , Classical , and Hellenistic periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek...
roots
{{Polytonic|ὀξύς}} (oxys) (
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
, literally "sharp," from the taste of acids) and
-γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. Chemists eventually determined that Lavoisier was wrong in this regard, but by that time it was too late, the name had taken. Actually, the gas that could more appropriately have been given the description, "acid producer," is hydrogen.
Oxygen entered the English language despite opposition by English scientists and the fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book
The Botanic GardenThe Botanic Garden is a set of two poems, The Economy of Vegetation and The Loves of the Plants, by the British poet and naturalist Erasmus Darwin. The Economy of Vegetation celebrates technological innovation, scientific discovery and offers theories concerning contemporary scientific questions,...
(1791) by
Erasmus DarwinErasmus Darwin was an English physician who turned down the invitation of George III for him to be a Royal Physician. He was also a natural philosopher, physiologist, abolitionist, inventor and poet...
, grandfather of
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
.
Later history
John DaltonJohn Dalton FRS was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness .-Early life:John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth in Cumberland,...
's original atomic hypothesis assumed that all elements were monoatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, giving the
atomic massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
of oxygen as 8 times that of hydrogen, instead of the modern value of about 16. In 1805,
Joseph Louis Gay-LussacJoseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries.- Biography :Gay-Lussac was born at...
and
Alexander von Humboldtwas a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher, and linguist, Wilhelm von Humboldt...
showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811
Amedeo AvogadroLorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto, Count of Quaregna and Cerreto was an Italian savant. He is most noted for his contributions to molecular theory, including what is known as Avogadro's law...
had arrived at the correct interpretation of water's composition, based on what is now called
Avogadro's lawAvogadro's law is a gas law named after Amedeo Avogadro who, in 1811, hypothesized that "Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of particles, or molecules." Thus, the number of molecules in a specific volume of gas is independent of...
and the assumption of diatomic elemental molecules.
By the late 19th century scientists realized that air could be liquefied, and its components isolated, by compressing and cooling it. Using a
cascadeIn chemical engineering, a cascade is a plant consisting of several similar stages with each processing the output from the previous stage. Cascades are most commonly used in isotope separation, distillation and other separation or purification processes....
method, Swiss chemist and physicist
Raoul Pierre PictetRaoul-Pierre Pictet was a Swiss physicist and the first person to liquefy nitrogen. He was born in Geneva and served as professor in the university of that city...
evaporatedEvaporation is the vaporization of a liquid and the reverse, of condensation. A type of phase transition, it is the process by which molecules in a liquid state spontaneously become gaseous . Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed...
liquid
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877 to the
French Academy of SciencesThe French Academy of Sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research...
in Paris announcing his discovery of
liquid oxygenLiquid oxygen is a form of the element oxygen. It has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horse shoe magnet...
. Just two days later, French physicist
Louis Paul CailletetLouis-Paul Cailletet was a French physicist and inventor.- Life and work :Cailletet was born in Châtillon-sur-Seine, Côte-d'Or. Educated in Paris, Cailletet returned to Chatillon to manage his father's ironworks...
announced his own method of liquefying molecular oxygen. Only a few drops of the liquid were produced in either case so no meaningful analysis could be conducted. Oxygen was liquified in stable state for the first time on March 29, 1877 by Polish scientists from
Jagiellonian UniversityThe Jagiellonian University was established in 1364 by Casimir III the Great in Kraków...
, Zygmunt Wróblewski and
Karol OlszewskiKarol Stanisław Olszewski was a Polish chemist, mathematician and physicist.-Life:...
.
In 1891 Scottish chemist
James DewarSir James Dewar FRS was a British chemist and physicist. He is probably best-known today for his invention of the Dewar flask, which he used in conjunction with extensive research into the liquefaction of gases...
was able to produce enough liquid oxygen to study. The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer
Carl von LindeProfessor Doctor Carl Paul Gottfried von Linde was a German engineer who developed refrigeration and gas separation technologies...
and British engineer William Hampson. Both men lowered the temperature of air until it liquefied and then
distilledDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
the component gases by boiling them off one at a time and capturing them. Later, in 1901, oxyacetylene
weldingWelding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
was demonstrated for the first time by burning a mixture of
acetyleneAcetylene is the chemical compound with the formula HC
2H. It is a hydrocarbon and the simplest alkyne. This colourless gas is widely used as a fuel and a chemical building block...
and compressed {{chem|O|2}}. This method of welding and cutting metal later became common.
In 1923 the American scientist
Robert H. GoddardRobert Hutchings Goddard , U.S. professor of physics and scientist, was a pioneer of controlled, liquid-fueled rocketry. He launched the world's first liquid-fueled rocket on March 16, 1926. From 1930 to 1935, he launched rockets that attained speeds of up to 885 km/h...
became the first person to develop a
rocket engineA rocket engine or simply "rocket" is a jet engine[Rocket Propulsion Elements; 7th edition- chapter 1] that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
; the engine used
gasolineGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines...
for fuel and liquid oxygen as the oxidizer. Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926 in
Auburn, MassachusettsAuburn is a town in Worcester County, Massachusetts, United States. The population was 15,901 at the 2000 census.- History :Auburn was first settled in 1714 and was officially incorporated in 1778 as the town of Ward, in honor of American Revolution General Artemas Ward...
, USA.
Industrial production
{{see also|Oxygen evolution|fractional distillation}}
Two major methods are employed to produce 100 million tonnes of {{chem|O|2}} extracted from air for industrial uses annually. The most common method is to
fractionally distillFractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
liquefied air into its various components, with nitrogen {{chem|N|2}}
distillingDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
as a vapor while oxygen {{chem|O|2}} is left as a liquid.
The other major method of producing {{chem|O|2}} gas involves passing a stream of clean, dry air through one bed of a pair of identical
zeoliteZeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
molecular sieves, which absorbs the nitrogen and delivers a gas stream that is 90% to 93% {{chem|O|2}}. Simultaneously, nitrogen gas is released from the other nitrogen-saturated zeolite bed, by reducing the chamber operating pressure and diverting part of the oxygen gas from the producer bed through it, in the reverse direction of flow. After a set cycle time the operation of the two beds is interchanged, thereby allowing for a continuous supply of gaseous oxygen to be pumped through a pipeline. This is known as
pressure swing adsorptionPressure Swing Adsorption is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation...
. Oxygen gas is increasingly obtained by these non-
cryogenicIn physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. Rather than the familiar temperature scales of Fahrenheit and Celsius, cryogenicists use the Kelvin scales...
technologies (see also the related
vacuum swing adsorptionVacuum swing adsorption is a non-cryogenic gas separation technology.Using special solids, or absorbents, VSA segregates certain gases from a gaseous mixture under minimal pressure according to the species' molecular characteristics and affinity for the absorbents...
).
Oxygen gas can also be produced through
electrolysis of waterElectrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water...
into molecular oxygen and hydrogen. DC electricity must be used: if AC is used, the gases in each limb consist of hydrogen and oxygen in the explosive ratio 2:1. Contrary to popular belief, the 2:1 ratio observed in the DC electrolysis of acidified water does not prove that the empirical formula of water is H2O unless certain assumptions are made about the molecular formulae of hydrogen and oxygen themselves.
A similar method is the electrocatalytic {{chem|O|2}} evolution from oxides and
oxoacidAn oxoacid is an acid which contains oxygen. More specifically, it is an acid which:#contains oxygen;#contains at least one other element;#has at least one hydrogen atom bound to oxygen; and#forms an ion by the loss of one or more protons....
s. Chemical catalysts can be used as well, such as in
chemical oxygen generatorA chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
s or oxygen candles that are used as part of the life-support equipment on submarines, and are still part of standard equipment on commercial airliners in case of depressurization emergencies. Another air separation technology involves forcing air to dissolve through
ceramicA ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
membranes based on
zirconium dioxideZirconium dioxide , sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral, baddeleyite...
by either high pressure or an electric current, to produce nearly pure {{chem|O|2}} gas.
In large quantities, the price of liquid oxygen in 2001 was approximately $0.21/kg. Since the primary cost of production is the energy cost of liquefying the air, the production cost will change as energy cost varies.
For reasons of economy, oxygen is often transported in bulk as a liquid in specially insulated tankers, since one
litreThe litre or liter is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case . The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau...
of liquefied oxygen is equivalent to 840 liters of gaseous oxygen at atmospheric pressure and 20 °
CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
. Such tankers are used to refill bulk liquid oxygen storage containers, which stand outside hospitals and other institutions with a need for large volumes of pure oxygen gas. Liquid oxygen is passed through
heat exchangerA heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
s, which convert the cryogenic liquid into gas before it enters the building. Oxygen is also stored and shipped in smaller
cylindersAn oxygen tank is a storage vessel for oxygen, which is either held under pressure in gas cylinders or as liquid oxygen in a cryogenic storage tank.Oxygen tanks are used to store gas for:* industrial processes including the manufacture of steel and methanol...
containing the compressed gas; a form that is useful in certain portable medical applications and
oxy-fuel welding and cuttingOxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively...
.
Medical
{{main|Oxygen therapy}}
Uptake of {{chem|O|2}} from the air is the essential purpose of
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
, so oxygen supplementation is used in
medicineMedicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
.
Oxygen therapyOxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
is used to treat
emphysemaEmphysema is a lung disease, characterized by an abnormal, permanent enlargement of air spaces distal to the terminal bronchioles. The disease is coupled with the destruction of walls, but without obvious fibrosis...
,
pneumoniaPneumonia is an inflammatory illness of the lung. Frequently, it is described as lung parenchyma/alveolar inflammation and abnormal alveolar filling with fluid ....
, some heart disorders, and any
diseaseA disease or medical condition isan abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs...
that impairs the body's ability to take up and use gaseous oxygen. Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices.
Oxygen tentthumb|300pxAn oxygen tent consists in a canopy placed over the head and shoulders or over the entire body of a patient to provide oxygen at a higher level than normal.-External links:*...
s were once commonly used in oxygen supplementation, but have since been replaced mostly by the use of
oxygen maskAn oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...
s or
nasal cannulaThe nasal cannula is a device used to deliver supplemental oxygen to a patient or person in need of extra oxygen. This device consists of a plastic tube which fits behind the ears, and a set of two prongs which are placed in the nostrils. Oxygen flows from these prongs...
s.
Hyperbaric (high-pressure) medicine uses special oxygen chambers to increase the
partial pressureIn a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of {{chem|O|2}} around the patient and, when needed, the medical staff.
Carbon monoxide poisoningCarbon monoxide poisoning occurs after enough inhalation of carbon monoxide . Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and non-irritating, it is very difficult for people to detect...
,
gas gangreneGas gangrene is a bacterial infection that produces gas within tissues in gangrene. It is a deadly form of gangrene usually caused by Clostridium bacteria. It is a medical emergency.-Features:...
, and
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
(the 'bends') are sometimes treated using these devices. Increased {{chem|O|2}} concentration in the lungs helps to displace
carbon monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
from the heme group of
hemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
. Oxygen gas is poisonous to the anaerobic bacteria that cause gas gangrene, so increasing its partial pressure helps kill them. Decompression sickness occurs in divers who decompress too quickly after a dive, resulting in bubbles of inert gas, mostly nitrogen and helium, forming in their blood. Increasing the pressure of {{chem|O|2}} as soon as possible is part of the treatment.
Oxygen is also used medically for patients who require
mechanical ventilationIn medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing.This may involve a machine called a ventilator or the breathing may be assisted by a physician or other suitable person compressing a bag or set of bellows...
, often at concentrations above 21% found in ambient air.
Life support and recreational use
A notable application of {{chem|O|2}} as a low-pressure
breathing gasBreathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
is in modern
space suitA space suit is a complex system of garments, equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space...
s, which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressure of {{chem|O|2}}. This trade-off of higher oxygen concentration for lower pressure is needed to maintain flexible spacesuits.
Scuba diverScuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons.Unlike early diving, which relied exclusively on air pumped from the surface, scuba...
s and
submarineA submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has only limited underwater capability...
rs also rely on artificially delivered {{chem|O|2}}, but most often use normal pressure, and/or mixtures of oxygen and air. Pure or nearly pure {{chem|O|2}} use in diving at higher-than-sea-level pressures is usually limited to rebreather, decompression, or emergency treatment use at relatively shallow depths (~6 meters depth, or less). Deeper diving requires significant dilution of {{chem|O|2}} with other gases, such as nitrogen or helium, to help prevent
oxygen toxicityOxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
.
People who climb mountains or fly in non-pressurized
fixed-wing aircraftA fixed-wing aircraft, usually called an airplane, aeroplane or plane, is an aircraft capable of flight using forward motion that causes air to pass over its wings to generate lift. Planes include jet engine and propeller driven vehicles propelled forward by thrust, as well as unpowered aircraft...
sometimes have supplemental {{chem|O|2}} supplies. Passengers traveling in (pressurized) commercial airplanes have an emergency supply of {{chem|O|2}} automatically supplied to them in case of cabin depressurization. Sudden cabin pressure loss activates
chemical oxygen generatorA chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
s above each seat, causing
oxygen maskAn oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...
s to drop and forcing iron filings into the
sodium chlorateSodium chlorate is a chemical compound with the chemical formula . When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic...
inside the canister. A steady stream of oxygen gas is produced by the
exothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light , electricity , or sound. Its etymology stems from the Greek prefix ex- and the Greek word thermein...
reaction. However, even this may pose a danger if inappropriately triggered: a
ValuJet airplaneValuJet Flight 592 was a flight that crashed on May 11, 1996 en route from Miami International Airport in Miami, Florida, United States, to William B. Hartsfield Atlanta International Airport in Atlanta, Georgia...
crashed after use-date-expired {{chem|O|2}} canisters, which were being shipped in the cargo hold, activated and caused fire. The canisters were mis-labeled as
empty, and carried against
dangerous goodsDangerous goods, also called hazardous materials or HazMat , are solids, liquids, or gases that can harm people, other living organisms, property, or the environment. They are often subject to chemical regulations...
regulations.
Oxygen, as a supposed mild
euphoricEuphoria is medically recognized as a mental/emotional state defined as a sense of great elation and wellbeing. Technically, euphoria is an affect, but the term is often colloquially used to define emotion as an intense state of transcendent happiness combined with an overwhelming sense of wellbeing...
, has a history of recreational use in
oxygen barAn oxygen bar is an establishment, or part of one, that sells oxygen for recreational use. Individual flavored scents may be added to enhance the experience...
s and in
sportSport is an activity that is governed by a set of rules or customs and often engaged in competitively. Sports commonly refer to activities where the physical capabilities of the competitor are the sole or primary determinant of the outcome , but the term is also used to include activities such as...
s. Oxygen bars are establishments, found in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
,
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
, and
Las Vegas, NevadaLas Vegas is the most populous city in the U.S. state of Nevada, the seat of Clark County, and an internationally renowned major resort city for gambling, shopping, fine dining, and entertainment. Las Vegas, which bills itself as The Entertainment Capital of the World, is famous for the number of...
since the late 1990s that offer higher than normal {{chem|O|2}} exposure for a fee. Professional athletes, especially in
American footballAmerican football, known in the United States and Canada simply as football, and often as Gridiron or Tackle football outside North America, is a competitive team sport known for combining strategy with physical play. The objective of the game is to score points by advancing the ball into the...
, also sometimes go off field between plays to wear oxygen masks in order to get a supposed "boost" in performance. However, the reality of a pharmacological effect is doubtful; a
placeboA placebo is a sham medical intervention. In one common placebo procedure, a patient is given an inert sugar pill, told that it may improve his/her condition, but not told that it is in fact inert...
or psychological boost being the most plausible explanation. Available studies support a performance boost from enriched {{chem|O|2}} mixtures only if they are breathed
during actual aerobic exercise. Other recreational uses include pyrotechnic applications, such as George Goble's five-second ignition of
barbecueBarbecue or barbeque is a method and apparatus for cooking meat, with the heat and hot gases of a fire, smoking wood, or hot coals of charcoal or a propane gas grill, and may...
grills.
Industrial
SmeltingSmelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
of
iron oreIron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of magnetite , hematite , goethite, limonite or...
into
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
consumes 55% of commercially produced oxygen. In this process, {{chem|O|2}} is injected through a high-pressure lance into molten iron, which removes
sulfurSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
impurities and excess
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
as the respective oxides, {{chem|SO|2}} and {{chem|CO|2}}. The reactions are
exothermicAn exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
, so the temperature increases to 1,700 °
CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
.
Another 25% of commercially produced oxygen is used by the chemical industry.
EthyleneEthylene is the chemical compound with the formula C
2H
4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin. It is extremely important in industry and also has a role in biology as a hormone...
is reacted with {{chem|O|2}} to create
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
, which, in turn, is converted into
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
; the primary feeder material used to manufacture a host of products, including
antifreezeAntifreeze is a cryoprotectant used in internal combustion engines, and for many other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from undergoing physical stresses and catastrophic deformation due to the...
and
polyesterPolyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
polymers (the precursors of many
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
s and
fabricA fabric is a textile material, and is short for "textile fabrication".Fabric may also refer to:*Fabric , the spatial and geometric configuration of elements within a rock*fabric , a nightclub in London, EnglandIn computing:...
s).
Most of the remaining 20% of commercially produced oxygen is used in medical applications, metal cutting and welding, as an oxidizer in rocket fuel, and in
water treatmentWater treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...
. Oxygen is used in oxyacetylene welding burning
acetyleneAcetylene is the chemical compound with the formula HC
2H. It is a hydrocarbon and the simplest alkyne. This colourless gas is widely used as a fuel and a chemical building block...
with {{chem|O|2}} to produce a very hot flame. In this process, metal up to 60
cmA centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the current SI base unit of length. Centi is the SI prefix for a factor of...
thick is first heated with a small oxy-acetylene flame and then quickly cut by a large stream of {{chem|O|2}}. Rocket propulsion requires a fuel and an oxidizer. Larger
rocketA rocket or rocket vehicle is a missile, spacecraft, aircraft or other vehicle which obtains thrust by the reaction of the rocket to the ejection of a jet of fast moving fluid exhaust from a rocket engine. Chemical rockets create their exhaust by the combustion of rocket propellant...
s use liquid oxygen as their oxidizer, which is mixed and ignited with the fuel for propulsion.
Scientific
PaleoclimatologistsPaleoclimatology is the study of climate change taken on the scale of the entire history of Earth. It uses records from ice sheets, tree rings, sediment, and rocks to determine the past state of the climate system on Earth....
measure the ratio of
oxygen-18Oxygen-18 is a natural, stable isotope of oxygen and one of the environmental isotopes.18O is an important precursor for the production of fluorodeoxyglucose used in positron emission tomography...
and oxygen-16 in the shells and
skeletonIn biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa. Exoskeletons are external, as is typical of many invertebrates; they enclose the soft tissues and organs of the...
s of marine organisms to determine what the climate was like millions of years ago (see
oxygen isotope ratio cycleOxygen isotope ratio cycles are cyclical variations in the ratio of the mass of oxygen with an atomic weight of 18 to the mass of oxygen with an atomic weight of 16 present in some substance, such as polar ice or calcite in ocean core samples. The ratio is linked to water temperature of ancient...
).
SeawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
molecules that contain the lighter
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
, oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18; this disparity increases at lower temperatures. During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and the seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate. Paleoclimatologists also directly measure this ratio in the water molecules of
ice coreAn ice core is a core sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods...
samples that are up to several hundreds of thousands of years old.
Planetary geologistsThe geology of solar terrestrial planets mainly deals with the geological aspects of four planets of the Solar system namely, Mercury, Venus, Earth, and Mars and one terrestrial dwarf planet, Ceres. Objects like Pluto are similar to terrestrial planets in the fact that they do have a solid surface,...
have measured different abundances of oxygen isotopes in samples from the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
, the
MoonThe Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is , about thirty times the diameter of the Earth. The common centre of mass of the system is located at about —a quarter the Earth's...
,
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
, and
meteoriteA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s, but were long unable to obtain reference values for the isotope ratios in the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
, believed to be the same as those of the primordial solar nebula. However, analysis of a
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
wafer exposed to the
solar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...
in space and returned by the crashed
Genesis spacecraftThe Genesis spacecraft collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA "sample return mission" to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon...
has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from the Sun's
disk of protoplanetary materialA protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star or Herbig star...
prior to the coalescence of dust grains that formed the Earth.
Oxygen presents two spectrophotometric
absorption bandAn absorption band is a range of wavelengths in the electromagnetic spectrum which are able to excite a particular transition in a substance. See absorption spectrum...
s peaking at the wavelengths 687 and 760
nmA nanometre is a unit of length in the metric system, equal to one billionth of a meter....
. Some
remote sensingRemote sensing is the small or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device that are wireless, or not in physical or intimate contact with the object...
scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a
satelliteEarth observation satellites are satellites specifically designed to observe Earth from orbit, similar toreconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. Geostationary satellites hover over the same spot, providing...
platform. This approach exploits the fact that in those bands it is possible to discriminate the vegetation's reflectance from its
fluorescenceFluorescence is the emission of visible light by a substance that has absorbed light of a differing, usually invisible, wavelength. Absorption of a photon triggers the emission of a photon with a longer wavelength. A shorter wavelength emission is sometimes observed from multiple photon absorption...
, which is much weaker. The measurement is technically difficult owing to the low
signal-to-noise ratioSignal-to-noise ratio is an electrical engineering measurement, also used in other fields , defined as the ratio of a signal power to the noise power corrupting the signal...
and the physical structure of vegetation; but it has been proposed as a possible method of monitoring the
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
from satellites on a global scale.
{{-}}
Compounds
{{main|Compounds of oxygen}}
The
oxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as
peroxideA peroxide is a compound containing an oxygen-oxygen single bond. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately.- Organic chemistry :...
s. Compounds containing oxygen in other oxidation states are very uncommon: −1/2 (
superoxideSuperoxide is an anion with the chemical formula O
2−. It is important as the product of the one-electron reduction of dioxygen O
2, which occurs widely in nature...
s), −1/3 (
ozonideOzonide is an unstable, reactive polyatomic anion O
3−, derived from ozone, or an organic compound similar to organic peroxide formed by a reaction of ozone with an unsaturated compound.-Inorganic ozonides:...
s), 0 (
elementalThere are several known allotropes of oxygen:*Free radicals O1 - unstable*dioxygen, O2 - colorless*ozone, O3 - blue*tetraoxygen, O4 - metastable...
,
hypofluorous acidHypofluorous acid is the chemical compound with the formula HFO. It is an intermediate in the oxidation of water by fluorine, which produces hydrogen fluoride and oxygen. It is the only hypohalic acid that can be isolated as a solid. HOF is explosive, decomposing to oxygen and HF...
), +1/2 (
dioxygenylThe dioxygenyl ion, , is a rarely-encountered oxycation in which both oxygen atoms have an oxidation state of +½. It is formally derived from oxygen by the removal of an electron:...
), +1 (
dioxygen difluorideDioxygen difluoride is a compound with the formula O
2F
2. This yellow compound is a strong oxidant and decomposes into OF
2 and oxygen even at −160 °C .-Preparation:...
), and +2 (
oxygen difluorideOxygen difluoride is the chemical compound with the formula OF2. As predicted by VSEPR theory, the molecule adopts a "V" shaped structure like H2O, but it has very different properties, being a strong oxidizer.-Preparation:...
).
Oxides and other inorganic compounds
WaterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
({{chem|H|2|O}}) is the oxide of
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
and the most familiar oxygen compound. Hydrogen atoms are covalently bonded to oxygen in a water molecule but also have an additional attraction (about 23.3 kJ·mol
−1 per hydrogen atom) to an adjacent oxygen atom in a separate molecule. These
hydrogen bondA hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, like nitrogen, oxygen or fluorine . The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s between water molecules hold them approximately 15% closer than what would be expected in a simple liquid with just
Van der Waals forceIn physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules...
s.
Due to its
electronegativityElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
, oxygen forms
chemical bondA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
s with almost all other elements at elevated temperatures to give corresponding
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s. However, some elements readily form oxides at
standard conditions for temperature and pressureIn physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data...
; the
rustRust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances...
ing of
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
is an example. The surface of metals like
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
and
titaniumTitanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other...
are oxidized in the presence of air and become coated with a thin film of oxide that
passivatesPassivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and...
the metal and slows further
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. Some of the
transition metal oxidesTransition metal oxides comprise a class of materials that contain transition elements and oxygen. They include insulators as well as metals. Often the same material may display both types of transport properties, hence a Metal-Insulator transition, obtained by varying either temperature or...
are found in nature as
non-stoichiometric compoundNon-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and therefore violate the law of definite proportions. Often, they are solids that contain crystallographic point defects, such as interstitial...
s, with a slightly less metal than the
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
would show. For example, the natural occurring
FeOIron oxide, also known as ferrous oxide, iron oxide/oxidized iron or more commonly rusted iron, is one of the iron oxides. It is a black-colored powder with the chemical formula . It consists of the chemical element iron in the oxidation state of 2 bonded to oxygen. Its mineral form is known as...
(
wüstiteWüstite is a mineral form of iron oxide found with meteorites and native iron. It has a gray color with a greenish tint in reflected light. Wüstite crystallizes in the isometric - hexoctahedral crystal system in opaque to translucent metallic grains. It has a Mohs hardness of 5 to 5.5 and a...
) is actually written as {{chem|Fe|1 −
x|O}}, where
x is usually around 0.05.
Oxygen as a compound is present in the atmosphere in trace quantities in the form of
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
({{chem|C||O|2}}). The earth's crustal
rockIn geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
is composed in large part of oxides of
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
(
silicaThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of ' and has been known for its hardness since antiquity. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms...
{{chem|Si||O|2}}, found in
graniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their...
and
sandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
),
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
(
aluminium oxideAluminium oxide is an amphoteric oxide of aluminium with the chemical formula
23. It is also commonly referred to as alumina, corundum, sapphire, ruby or aloxite in the mining, ceramic and materials science communities. It is produced by the Bayer process from bauxite...
{{chem|Al|2|O|3}}, in
bauxiteBauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al
3, boehmite γ-AlO, and diaspore α-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO
2...
and
corundumCorundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present...
), iron (
iron(III) oxideIron oxide—also known as ferric oxide, ferric iron, hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust—is one of the several oxide compounds of iron, and has paramagnetic properties...
{{chem|Fe|2|O|3}}, in
hematiteHematite, also spelled as hæmatite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
and
rustRust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances...
) and other
metalA metal is a chemical element that is a good conductor of both electricity and heat, forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions...
s.
The rest of the Earth's crust is also made of oxygen compounds, in particular
calcium carbonateCalcium carbonate is a chemical compound with the chemical formula CaCO
3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural...
(in
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
) and
silicateA silicate is a compound containing an ion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2−, but the silicate species that are encountered most often...
s (in
feldsparFeldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
s). Water-
solubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure...
silicates in the form of {{chem|Na|4|Si||O|4}}, {{chem|Na|2|Si||O|3}}, and {{chem|Na|2|Si|2|O|5}} are used as
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s and
adhesiveAdhesive or glue is a compound in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry...
s.
Oxygen also acts as a ligand for transition metals, forming metal–{{chem|O|2}} bonds with the
iridiumIridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
atom in
Vaska's complexVaska's complex is the trivial name for the chemical compound trans-chlorocarbonylbisiridium, which has the formula IrCl[P3]2...
, with the
platinumPlatinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements...
in
{{otheruses4|the chemical element and its most stable form, {{chem|O|2}} or dioxygen|other forms of this element|Allotropes of oxygen|other uses|Oxygen (disambiguation)}}
{{pp-semi-vandalism|small=yes}}
Oxygen ({{pron-en|ˈɒksɨdʒɨn}}, {{respell|OK|si-jin}}, from the GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
roots ὀξύς (oxys) (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the
elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
with
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
8 and represented by the symbol
O. It is a member of the
chalcogenThe chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
group on the
periodic tableThe periodiс table of the chemical elements is a tabular display of the chemical elements...
, and is a highly reactive
nonmetalNonmetal, or non-metal, is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal...
lic
period 2 elementA period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical...
that readily forms
compoundsA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
(notably
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s) with almost all other elements. At standard temperature and pressure two atoms of the element
bindA chemical bond is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction...
to form dioxygen, a colorless, odorless, tasteless diatomic
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
with the formula {{chem|O|2}}. Oxygen is the
third most abundantThe abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. Abundance may be variously measured by the mass-fraction , or mole-fraction , or by volume fraction...
element in the universe by mass after
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
and
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
and the
most abundant-Earth bulk continental crust and upper continental crust:*C1 — Crust: CRC Handbook*C2 — Crust: Kaye & Laby*C3 — Crust: Greenwood*C4 — Crust: Ahrens *C5 — Crust: Ahrens...
element by mass in the Earth's crust. Diatomic oxygen gas constitutes 20.9% of the volume of
airThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
.
All major classes of structural molecules in living organisms, such as
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s,
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s, and
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s, contain oxygen, as do the major
inorganic compoundTraditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin...
s that comprise animal shells, teeth, and bone. Oxygen in the form of {{chem|O|2}} is produced from water by
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
,
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
and plants during
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
and is used in
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
for all complex life. Oxygen is toxic to
obligately anaerobic organismsObligate anaerobes are anaerobic organisms that fail to grow in the presence of oxygen.-Metabolism:Obligate anaerobes die in presence of oxygen due to the absence of the enzymes superoxide dismutase and catalase, which would convert the lethal superoxide formed in their cells due to the presence...
, which were the dominant form of
early lifeThe evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved. It stretches back over , possibly as far as , and evolution continues, even in humans. All present-day organisms use the same large set of complex chemical reactions, which indicates that...
on Earth until {{chem|O|2}} began to accumulate in the atmosphere 2.5 billion years ago. Another form (
allotropeThere are several known allotropes of oxygen:*Free radicals O1 - unstable*dioxygen, O2 - colorless*ozone, O3 - blue*tetraoxygen, O4 - metastable...
) of oxygen,
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
({{chem|O|3}}), helps protect the biosphere from ultraviolet radiation with the high-altitude
ozone layerThe ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here...
, but is a pollutant near the surface where it is a by-product of
smogSmog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide...
. At even higher
low earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
altitudes atomic oxygen is a significant presence and a cause of
erosion for spacecraftCorrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet light and x-rays, high-energy charged particles...
.
Oxygen was independently discovered by
Carl Wilhelm ScheeleCarl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
, in
UppsalaUppsala is the capital of Uppsala County and the fourth largest city of Sweden with 144,839 inhabitants....
, in 1773 or earlier, and
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
in
WiltshireWiltshire is a ceremonial county in the south west of England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers 3,485 km²...
, in 1774, but Priestley is often given priority because his publication came out in print first. The name
oxygen was coined in 1777 by
Antoine LavoisierAntoine-Laurent de Lavoisier ; ), the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology...
, whose experiments with oxygen helped to discredit the then-popular
phlogiston theoryThe phlogiston theory , first stated in 1667 by Johann Joachim Becher, is a defunct scientific theory that posited the existence of a fire-like element called "phlogiston" that was contained within combustible bodies, and released during combustion...
of
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
and
corrosion