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Empirical formula

 

 
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Empirical formula
 
 
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In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, the empirical formula of a chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 is a complex expression of the relative numbers of each type of atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
 in it. An empirical formula makes references to isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
ism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic compounds, such as CaCl2
Calcium chloride

Calcium chloride, CaCl2, is a common Salt . It behaves as a typical ionic halide, and is solid at room temperature. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in concrete....
, and for macromolecules, such as SiO2
Silicon dioxide

The 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....
. The term empirical refers to the process of elemental analysis
Elemental analysis

Elemental analysis is a process where a sample of some material is analyzed for its chemical element and sometimes isotope composition. Elemental analysis can be qualitative , and it can be quantitative ....
, a technique of analytical chemistry
Analytical chemistry

Analytical chemistry is the study of the chemical composition of natural and artificial materials. Unlike other major sub disciplines of chemistry such as inorganic chemistry and organic chemistry, analytical chemistry is not restricted to any particular type of chemical compound or chemical reaction....
 used to determine the relative amounts of each element in a chemical compound.

In contrast, the molecular formula identifies a numbers of each type of atom in a compound, and the structural formula
Structural formula

The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly....
 also shows the structure of the molecule.

For example, the chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 n-hexane has the structural formula
Structural formula

The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly....
  CH3CH2CH2CH2CH2CH3, which shows that it has 7 carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 atoms arranged in a straight chain, and 14 hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 atoms. Hexane's molecular formula is C6H14, and its empirical formula is C3H7, showing a C:H ratio of 4:9.

le class="wikitable">
Substance Molecular formula Empirical formula
Water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 H2O H2O
Methane
Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
 CH4 CH4
Benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
 C6H6 CH
Sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
 S8 S
Glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 C6H12O6 CH2O


a class="link1" onMouseover='showByLink("m560088",this)' onMouseout='hide("m560088")'href="http://www.absoluteastronomy.com/topics/Physics">physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, an empirical formula is a mathematical equation
Equation

An equation is a mathematics Proposition, in table of mathematical symbols, that two things are exactly the same . Equations are written with an equal sign, as in...
 that predicts observed results, but is derived from experiment or conjecture and not directly from first principles.

An example was the Rydberg formula
Rydberg formula

The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. The formula was invented by the Swedish physicist Johannes Rydberg and presented on November 5, 1888....
 to predict the wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
s of hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 spectral line
Spectral line

A spectral line is a dark or bright line in an otherwise uniform and continuous optical spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies....
s.






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Encyclopedia


In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, the empirical formula of a chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 is a complex expression of the relative numbers of each type of atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
 in it. An empirical formula makes references to isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
ism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic compounds, such as CaCl2
Calcium chloride

Calcium chloride, CaCl2, is a common Salt . It behaves as a typical ionic halide, and is solid at room temperature. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in concrete....
, and for macromolecules, such as SiO2
Silicon dioxide

The 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....
. The term empirical refers to the process of elemental analysis
Elemental analysis

Elemental analysis is a process where a sample of some material is analyzed for its chemical element and sometimes isotope composition. Elemental analysis can be qualitative , and it can be quantitative ....
, a technique of analytical chemistry
Analytical chemistry

Analytical chemistry is the study of the chemical composition of natural and artificial materials. Unlike other major sub disciplines of chemistry such as inorganic chemistry and organic chemistry, analytical chemistry is not restricted to any particular type of chemical compound or chemical reaction....
 used to determine the relative amounts of each element in a chemical compound.

In contrast, the molecular formula identifies a numbers of each type of atom in a compound, and the structural formula
Structural formula

The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly....
 also shows the structure of the molecule.

For example, the chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 n-hexane has the structural formula
Structural formula

The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly....
  CH3CH2CH2CH2CH2CH3, which shows that it has 7 carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 atoms arranged in a straight chain, and 14 hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 atoms. Hexane's molecular formula is C6H14, and its empirical formula is C3H7, showing a C:H ratio of 4:9.

Examples of common substances

Substance Molecular formula Empirical formula
Water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 H2O H2O
Methane
Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
 CH4 CH4
Benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
 C6H6 CH
Sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
 S8 S
Glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 C6H12O6 CH2O


Use in physics

In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, an empirical formula is a mathematical equation
Equation

An equation is a mathematics Proposition, in table of mathematical symbols, that two things are exactly the same . Equations are written with an equal sign, as in...
 that predicts observed results, but is derived from experiment or conjecture and not directly from first principles.

An example was the Rydberg formula
Rydberg formula

The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. The formula was invented by the Swedish physicist Johannes Rydberg and presented on November 5, 1888....
 to predict the wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
s of hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 spectral line
Spectral line

A spectral line is a dark or bright line in an otherwise uniform and continuous optical spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies....
s. Proposed in 1888, it perfectly predicted the wavelengths of the Lyman series
Lyman series

In physics, the Lyman series is the series of transitions and resulting emission lines of the hydrogen atom as an electron goes from n = 2 to n = 1 ....
, but it was not clear why it worked until Niels Bohr
Niels Bohr

Niels Henrik David Bohr was a Denmark physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922....
 produced his Bohr model
Bohr model

In atomic physics, the Bohr model created by Niels Bohr depicts the atom as a small, positively charged atomic nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity....
 of the atom in 1913.

Construction of empirical formulas for prediction of experimental data is considered by M.Ribaric and L.Sustersic in http://arxiv.org/pdf/0810.0905 so as to point out relevant technical problems.

See also


  • Empiricism
    Empiricism

    In philosophy, empiricism is a theory of knowledge which asserts that knowledge arises from experience. Empiricism is one of several competing views about how we know "things," part of the branch of philosophy called epistemology, or "theory of knowledge"....
     (Philosophic usage and history)
  • Empirical research
    Empirical research

    Empirical research is any research that bases its findings on direct or indirect observation as its test of reality. Such research may also be conducted according to Hypothetico deductive model procedures, such as those developed from the work of Ronald Fisher....
     (More on the scientific usage)
  • Empirical
    Empirical

    The word empirical denotes information gained by means of observation, experience, or experiment, as opposed to theory. A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or Logical consequence that are observable by the senses....
  • Phenomenology
    Phenomenology (science)

    The term phenomenology in science is used to describe a body of knowledge which relates experiment of phenomenon to each other, in a way which is consistent with fundamental theory, but is not directly derived from theory....