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Tellurium is a chemical element
Chemical element
A 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. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 that has the symbol Te and atomic number
Atomic number
In 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...

 52. A brittle, mildly toxic, rare, silver-white metalloid
Metalloid
Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...

 which looks similar to tin
Tin
Tin 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 and has two possible oxidation states, +2 and the slightly more stable +4...

, tellurium is chemically related to selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

. It is occasionally found in native form, as elemental crystals. Tellurium is far more common in the universe than on Earth. Its extreme rarity
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...

 in the Earth's crust, comparable to that of platinum, is partly due to its high atomic number, but also due to its formation of a volatile hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

 which caused the element to be lost to space as a gas during the hot nebular formation of the planet.

Tellurium was discovered in Transylvania
Transylvania
Transylvania is a historical region in the central part of Romania. Bounded on the east and south by the Carpathian mountain range, historical Transylvania extended in the west to the Apuseni Mountains; however, the term sometimes encompasses not only Transylvania proper, but also the historical...

 (today part of Romania
Romania
Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

) in 1782 by Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller Freiherr von Reichenstein or Franz-Joseph Müller von Reichenstein was an Austrian mineralogist and mining engineer. Müller held several positions in the Austria-Hungarian administration of mines and coinage in the Banat, Transylvania, and Tyrol...

 in a mineral containing tellurium and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

. Martin Heinrich Klaproth
Martin Heinrich Klaproth
Martin Heinrich Klaproth was a German chemist.Klaproth was born in Wernigerode. During a large portion of his life he followed the profession of an apothecary...

 named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals (responsible for the name of Telluride, Colorado
Telluride, Colorado
The town of Telluride is the county seat and most populous town of San Miguel County in the southwestern portion of the U.S. state of Colorado. The town is a former silver mining camp on the San Miguel River in the western San Juan Mountains...

) are the most notable natural gold compounds. However, they are not a commercially significant source of tellurium itself, which is normally extracted as by-product of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 production.

Tellurium is commercially primarily used in alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

s, foremost in steel and copper to improve machinability. Applications in solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s and as a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 material also consume a considerable fraction of tellurium production.

Tellurium has no biological function, although fungi can incorporate it in place of sulfur and selenium into amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s such as telluro-cysteine and telluro-methionine. In humans, tellurium is partly metabolized into dimethyl telluride, (CH3)2Te, a gas with a garlic
Garlic
Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...

-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.

Physical properties


When crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line, tellurium is silvery-white and when it is in pure state it has a metallic luster. It is a brittle and easily pulverized metalloid. Amorphous tellurium is found by precipitating it from a solution of tellurous or telluric acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 (Te(OH)6). Tellurium is a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 that shows a greater electrical conductivity in certain directions which depends on atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

ic alignment; the conductivity increases slightly when exposed to light (photoconductivity
Photoconductivity
Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation....

). When in its molten state, tellurium is corrosive to copper, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

.

Chemical properties


Tellurium adopts a polymeric structure, consisting of zig-zag chains of Te atoms. This gray material resists oxidation by air and is nonvolatile.

Isotopes



Naturally occurring tellurium has eight isotopes. Four of those isotopes, 122Te, 124Te, 125Te and 126Te, are stable. The other four, 120Te, 123Te, 128Te and 130Te, have been observed to be radioactive. The stable isotopes make up only 33.2 % of the naturally occurring tellurium; this is possible due to the long half-lives of the unstable isotopes. They are in the range from 1013 to 2.2 1024 years (for 128Te). This makes 128Te the isotope with the longest half life among all radionuclide
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...

s., which is approximately 160 trillion (1012) times the age of known universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...

.

There are 38 known nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...

s of tellurium with atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....

es that range from 105 to 142. Tellurium is among the lightest elements known to undergo alpha decay, with isotopes 106Te to 110Te being able to undergo this mode of decay. The atomic mass of tellurium (127.60 g·mol−1) exceeds that of the following element iodine (126.90 g·mol−1).

Occurrence




With an abundance in the Earth's crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

 comparable to that of platinum
Platinum
Platinum 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 a dense, malleable, ductile, precious, gray-white transition metal...

, tellurium is one of the rarest stable solid elements in the Earth's crust. Its abundance is about 1 µg/kg. In comparison, even the rarest of the lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...

s have crustal abundances of 500 µg/kg (see Abundance of the chemical elements
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...

).

The extreme rarity of tellurium in the Earth's crust is not a reflection of its cosmic abundance, which is in fact greater than that of rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

, even though rubidium is ten thousand times more abundant in the Earth's crust. The extraordinarily low abundance of tellurium on Earth is rather thought to be due to conditions in the Earth's formation, when the stable form of certain elements, in the absence of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, was controlled by the reductive power of free hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. Under this scenario, certain elements such as tellurium which form volatile hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

s were severely depleted during the formation of the Earth's crust, through evaporation of these hydrides. Tellurium and selenium are the heavy elements most depleted in the Earth's crust by this process.

Tellurium is sometimes found in its native (elemental) form, but is more often found as the tellurides of gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 (calaverite
Calaverite
Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...

, krennerite
Krennerite
Krennerite is an orthorhombic gold telluride mineral which can contain a relatively small amount of silver in the structure. The formula is AuTe2 varying to Te2. Both of the chemically similar gold-silver tellurides, calaverite and sylvanite are in the monoclinic crystal system, whereas krennerite...

, petzite
Petzite
The mineral petzite, Ag3AuTe2, is a soft, steel-gray telluride mineral generally deposited by hydrothermal activity. It forms isometric crystals, and is usually associated with rare tellurium and gold minerals, often with silver, mercury, and copper....

, sylvanite
Sylvanite
Sylvanite or silver gold telluride, Te2, is the most common telluride of gold.-Properties:The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with...

 and others). Tellurium compounds are the most common chemical compounds of gold found in nature (rare non-tellurides such as gold aurostibite
Aurostibite
Aurostibite is an isometric gold antimonide mineral which is a member of the pyrite group. Aurostibite was discovered in 1952 and can be found in hydrothermal gold-quartz veins, in sulfur-deficient environments that contain other antimony minerals. The mineral can be found in Yellowknife in the...

 and bismuthide
Bismuthide
The bismuthide ion is Bi3−.Bismuthides are compounds of bismuth with more electropositive elements. They are intermetallic compounds, containing partially metallic and partially ionic bonds....

 are known). Tellurium is also found combined with elements other than gold, in salts of other metals. In contrast to selenium, tellurium is not able to replace sulfur in its minerals. This is due to the large difference in ion radius of sulfur and tellurium. In consequence, many sulfide minerals contain considerable amounts of selenium, but only traces of tellurium.

In the gold rush of 1893, diggers in Kalgoorlie discarded a pyritic material which got in their way as they searched for pure gold. The Kalgoorlie waste was thus used to fill in potholes or as part of sidewalks. Three years passed before it was realized that this waste was calaverite
Calaverite
Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...

, a telluride of gold that had not been recognized. This led to a second gold rush in 1896 which included mining the streets.

Production


The principal source of tellurium is from anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

 sludge
Sludge
Sludge refers to the residual, semi-solid material left from industrial wastewater, or sewage treatment processes. It can also refer to the settled suspension obtained from conventional drinking water treatment, and numerous other industrial processes...

s produced during the electrolytic refining of blister copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

. It is a component of dusts from blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...

 refining of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

. Treatment of 500 tons of copper ore typically yields one pound (0.45 kg) of tellurium. Tellurium is produced mainly in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, 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...

 and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

. For the year 2006 the British Geological Survey
British Geological Survey
The British Geological Survey is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...

 gives the following numbers: United States 50 t, Peru 37 t, Japan 24 t and Canada 11 t.

The anode sludges contain the selenide
Selenide
A selenide is a chemical compound in which selenium serves as an anion with oxidation number of −2 , much as sulfur does in a sulfide. The chemistry of the selenides and sulfides are similar....

s and tellurides of the noble metals in compounds with the formula M2Se or M2Te (M = Cu, Ag, Au). At temperatures of 500 °C the anode sludges are roasted with sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 under air. The metal ions are reduced to the metals, while the telluride is converted to sodium tellurite
Sodium tellurite
Sodium tellurite is an inorganic tellurium compound with formula Na2TeO3. It is a water soluble white solid and a weak reducing agent. Sodium tellurite is an intermediate in the extraction of the element, tellurium; it is a mineral obtained from slimes and is a precursor to...

.
M2Te + O2 + Na2CO3 → Na2TeO3 + 2 M + CO2


Tellurite
Tellurite (ion)
The tellurite ion is TeO32−. A tellurite is a compound that contains this ion. An example is sodium tellurite. Tellurites are one of the more stable tellurium compounds, although they can be reduced to elemental tellurium by electrolysis or a strong reducing agent.-Acidified forms:In...

s can be leached from the mixture with water and are normally present as hydrotellurites HTeO3 in solution. Selenite
Selenite (ion)
The selenite anion is a selenium oxoanion with the chemical formula SeO32−.A selenite is a compound that contains this ion....

s are also formed during this process, but they can be separated by adding sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

. The hydrotellurites are converted into the insoluble tellurium dioxide
Tellurium dioxide
Tellurium dioxide is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO2, and the synthetic, colourless tetragonal , α-TeO2...

 while the selenites stay in solution.
HTeO3 + OH + H2SO4 → TeO2 + 2 SO42− + 2 H2O


The reduction to the metal is done either by electrolysis or by reacting the tellurium dioxide
Tellurium dioxide
Tellurium dioxide is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO2, and the synthetic, colourless tetragonal , α-TeO2...

 with sulfur dioxide in sulfuric acid.
TeO2 + 2 SO2 + 2H2O → Te + SO42− + 4 H+


Commercial-grade tellurium is usually marketed as 200-mesh
Mesh (scale)
Mesh material is often used in determining the particle size distribution of a granular material. For example, a sample from a truckload of peanuts may be placed atop a mesh with 5 mm openings. When the mesh is shaken, small broken pieces and dust pass through the mesh while whole peanuts are...

 powder but is also available as slabs, ingots, sticks, or lumps. The year-end price for tellurium in 2000 was US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

14 per pound. In recent years, the tellurium price was driven up by increased demand and limited supply, reaching as high as US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

100 per pound in 2006. Despite an expected doubling in production due to improved extraction methods, the United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

 (DoE) anticipates a supply shortfall of tellurium by 2025.

Compounds



Tellurium belongs to the same chemical family as oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 and polonium
Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...

: the chalcogen
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...

 family. Tellurium and selenium compounds are similar. It exhibits the oxidation states −2, +2, +4 and +6, with the +4 state being most common.

Tellurides
Reduction of Te metal produces the telluride
Telluride (chemistry)
The telluride ion is Te2−. It is the final stable member of the series of dianions O2−, S2−, and Se2− ....

s and polytellurides, Ten2–. The −2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, , formed by heating tellurium with zinc. Decomposition of with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

 yields hydrogen telluride
Hydrogen telluride
Hydrogen telluride is the inorganic compound with the formula H2Te. The simplest hydride of tellurium, it is rarely encountered because of it decomposes rapidly to the constituent elements. Most compounds with Te-H bonds are unstable with respect to loss of H2. H2Te is chemically and structurally...

 , a highly unstable analogue of the other chalcogen hydrides, ,
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 and
Hydrogen selenide
Hydrogen selenide is the inorganic compound with the formula H2Se. It is the simplest and virtually the only hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit: 0.05 ppm over an 8 hour period...

:
ZnTe + 2 HCl → +


is unstable, whereas salts of its conjugate base [TeH] are stable.

Halides
The +2 oxidation state is exhibited by the dihalides, , and . The dihalides have not been obtained in pure form, although they are known decomposition products of the tetrahalides in organic solvents, and their derived tetrahalotellurates are well-characterized:
Te + + 2 →


where X is Cl, Br, or I. These anions are square planar in geometry. Polynuclear anionic species also exist, such as the dark brown , and the black .

Fluorine forms two halides with tellurium: the mixed-valence and
Tellurium hexafluoride
Tellurium hexafluoride is the oldest known fluoride of tellurium. It is a colorless, highly toxic gas with an extremely unpleasant smell.-Preparation:...

. In the +6 oxidation state, the structural group occurs in a number of compounds such as
Teflic acid
Teflic acid is the chemical compound with the formula HOTeF5. This strong acid is related to orthotelluric acid, Te6. Teflic acid has octahedral geometry and, Ignoring its bent Te-O-H bond, has point group symmetry C4v.-Preparation:...

, , , and . The square antiprism
Square antiprism
In geometry, the square antiprism is the second in an infinite set of antiprisms formed by an even-numbered sequence of triangle sides closed by two polygon caps...

atic anion is also attested. The other halogens do not form halides with tellurium in the +6 oxidation state, but only tetrahalides (
Tellurium tetrachloride
Tellurium tetrachloride is the inorganic compound with the empirical formula TeCl4. The compound is volatile, subliming at 200 °C at 0.1 mm Hg. Molten TeCl4 is ionic, dissociating into ions TeCl3+ and Te2Cl102−.-Structure:...

,
Tellurium tetrabromide
Tellurium tetrabromide is an inorganic chemical compound. It has a similar tetrameric structure to TeCl4. It can be made by reacting bromine and tellurium.. In the vapour TeBr4 dissociates :It is a conductor when molten, dissociating into the ions TeBr3+ and Br−Solutions in benzene and...

 and
Tellurium tetraiodide
Tellurium tetraiodide is an inorganic chemical compound. It has a tetrameric structure which is different from the tetrameric solid forms of TeCl4 and TeBr4. In TeI4 the Te atoms are octahedrally coordinated and edges of the octahedra are shared....

) in the +4 state, and other lower halides . In the +4 oxidation state, halotellurate anions are known, such as and . Halotellurium cations are also attested, including , found in .

Oxocompounds

Tellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of in vacuum, disproportionating into tellurium dioxide
Tellurium dioxide
Tellurium dioxide is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO2, and the synthetic, colourless tetragonal , α-TeO2...

, and elemental tellurium upon heating. Since then, however, some doubt has been cast on its existence in the solid phase, although it is known as a vapor phase fragment; the black solid may be merely an equimolar mixture of elemental tellurium and tellurium dioxide.

Tellurium dioxide is formed by heating tellurium in air, causing it to burn with a blue flame. Tellurium trioxide, β-, is obtained by thermal decomposition of . The other two forms of trioxide reported in the literature, the α- and γ- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of , and . Tellurium also exhibits mixed-valence oxides, and .

The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid
Tellurous acid
Tellurous acid is an inorganic compound with the formula H2TeO3. It is the oxoacid of tellurium. The compound is not well characterized. An alternative way of writing its formula is 2TeO. In principle, tellurous acid would form by treatment of tellurium dioxide with water, i.e. hydrolysis...

 , orthotelluric acid
Telluric acid
Telluric acid is a chemical compound with the formula Te6. It is a white solid made up of octahedral Te6 molecules which persist in aqueous solution...

  and metatelluric acid . The two forms of telluric acid form tellurate salts containing the TeO and TeO anions, respectively. Tellurous acid forms tellurite salts containing the anion TeO. Other tellurium cations include , which consists of two fused tellurium rings and the polymeric .

Zintl cations
When tellurium is treated with concentrated sulfuric acid, it forms red solutions containing the Zintl ion, . The oxidation of tellurium by
Arsenic pentafluoride
Arsenic pentafluoride is a chemical compound of arsenic and fluorine. The oxidation state of arsenic is +5.-Synthesis:Arsenic pentafluoride can be prepared by direct combination of arsenic and fluorine:...

 in liquid
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 also produces this square planar cation, as well as with the trigonal prismatic, yellow-orange :
4 Te + 3 → +
6 Te + 6 → + 2


Other tellurium Zintl cations include the polymeric and the blue-black , which consists of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride
Tungsten hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten compounds. WCl6 is a rare example of a...

:
8 Te + 2 →


Interchalcogen cations also exist, such as (distorted cubic geometry) and . These are formed by oxidizing mixtures of tellurium and selenium with or
Antimony pentafluoride
Antimony pentafluoride is the inorganic compound with the formula SbF5. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, the strongest known acid...

.

Organotellurium compounds

Tellurium does not readily form analogues of alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s and thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

s, with the functional group –TeH and are called tellurol
Tellurol
Tellurols are analogues of alcohols and phenols where tellurium replaces oxygen. Tellurols, selenol, and thiols have similar properties, but tellurols are the least stable. Although they are fundamental representatives of organotellurium compounds, tellurols are lightly studied because of their...

s. The –TeH functional group is also attributed to using the prefix tellanyl-. Like H2Te
Hydrogen telluride
Hydrogen telluride is the inorganic compound with the formula H2Te. The simplest hydride of tellurium, it is rarely encountered because of it decomposes rapidly to the constituent elements. Most compounds with Te-H bonds are unstable with respect to loss of H2. H2Te is chemically and structurally...

, these species are unstable with respect to loss of hydrogen. Telluraethers (R-Te-R) are more stable as are telluroxide
Telluroxide
Telluroxide is a type of organotellurium compound with the formula R2TeO. These compounds are analogous to sulfoxides in some respects. Reflecting the decreased tendency of Te to form multiple bonds, telluroxides exist both the monomer and the polymer, which are favored in solution and the solid...

s.

History


Tellurium (Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 tellus meaning "earth") was discovered in the 18th century in a gold ore from the mines in Zlatna
Zlatna
Zlatna is a town in Alba County, central Transylvania, Romania. It has a population of 8,607.- Administration :The town administers eighteen villages: Boteşti , Budeni , Dealu Roatei , Dobrot, Dumbrava, Feneş , Galaţi , Izvoru Ampoiului , Pârău Gruiului , Pătrângeni ,...

, near what is now Sibiu
Sibiu
Sibiu is a city in Transylvania, Romania with a population of 154,548. Located some 282 km north-west of Bucharest, the city straddles the Cibin River, a tributary of the river Olt...

, Transylvania
Transylvania
Transylvania is a historical region in the central part of Romania. Bounded on the east and south by the Carpathian mountain range, historical Transylvania extended in the west to the Apuseni Mountains; however, the term sometimes encompasses not only Transylvania proper, but also the historical...

. This ore was known as "Faczebajer weißes blättriges Golderz" (white leafy gold ore from Faczebaja) or antimonalischer Goldkies (antimonic gold pyrite), and, according to Anton von Rupprecht, was Spießglaskönig (argent molybdique), containing native antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...

. In 1782 Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller Freiherr von Reichenstein or Franz-Joseph Müller von Reichenstein was an Austrian mineralogist and mining engineer. Müller held several positions in the Austria-Hungarian administration of mines and coinage in the Banat, Transylvania, and Tyrol...

, who was then serving as the Austrian chief inspector of mines in Transylvania, concluded that the ore did not contain antimony, but that it was bismuth sulfide. The following year, he reported that this was erroneous and that the ore contained mostly gold and an unknown metal very similar to antimony. After a thorough investigation which lasted for three years and consisted of more than fifty tests, Müller determined the specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 of the mineral and noted the radish
Radish
The radish is an edible root vegetable of the Brassicaceae family that was domesticated in Europe, in pre-Roman times. They are grown and consumed throughout the world. Radishes have numerous varieties, varying in size, color and duration of required cultivation time...

-like odor of the white smoke which passed off when the new metal was heated, the red color which the metal imparts to sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

, and the black precipitate which this solution gives when diluted with water. Nevertheless, he was not able to identify this metal and gave it the names aurum paradoxium and metallum problematicum, as it did not show the properties predicted for the expected antimony.

In 1789, another Hungarian scientist, Pál Kitaibel
Pál Kitaibel
Pál Kitaibel was a Hungarian botanist and chemist.He was born at Mattersburg and studied botany and chemistry at the undersity of Buda. He became professor taught these subjects at Pest in 1794...

, also discovered the element independently in an ore from Deutsch-Pilsen which had been regarded as argentiferous molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...

, but later he gave the credit to Müller. In 1798, it was named by Martin Heinrich Klaproth
Martin Heinrich Klaproth
Martin Heinrich Klaproth was a German chemist.Klaproth was born in Wernigerode. During a large portion of his life he followed the profession of an apothecary...

 who earlier isolated it from the mineral calaverite
Calaverite
Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...

. The 1960s brought growth in thermoelectric applications for tellurium (as bismuth telluride
Bismuth telluride
Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which, when alloyed with antimony or selenium is an efficient thermoelectric material for refrigeration or portable power generation...

), as well as its use in free-machining steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, which became the dominant use.

Metallurgy


The largest consumer of tellurium is metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

, where it is used in iron, copper and lead alloys.
When added to stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 it makes these metals more machinable. It is alloyed into cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 for promoting chill for spectroscopic purposes, as the presence of electrically conductive free graphite tends to deleteriously affect spark emission testing results. In lead it improves strength and durability and decreases the corrosive action of sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

.

Semiconductor and electronic industry uses



Tellurium is used in cadmium telluride
Cadmium telluride
Cadmium telluride is a crystalline compound formed from cadmium and tellurium. It is used as an infrared optical window and a solar cell material. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell...

 (CdTe) solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s. National Renewable Energy Laboratory
National Renewable Energy Laboratory
The National Renewable Energy Laboratory , located in Golden, Colorado, is the United States' primary laboratory for renewable energy and energy efficiency research and development. The National Renewable Energy Laboratory is a government-owned, contractor-operated facility; it is funded through...

 lab tests using this material achieved some of the highest efficiencies for solar cell electric power generation. Massive commercial production of CdTe solar panels
Cadmium telluride photovoltaics
Cadmium telluride photovoltaics describes a photovoltaic technology that is based on the use of cadmium telluride thin film, a semiconductor layer designed to absorb and convert sunlight into electricity...

 by First Solar
First Solar
First Solar, Inc. is an American manufacturer of thin film photovoltaic modules, or solar panels, and a provider to PV power plants of supporting services that include finance, construction, maintenance and end-of-life panel recycling...

 in recent years has significantly increased tellurium demand. If some of the cadmium in CdTe is replaced by zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 then (Cd,Zn)Te
Cadmium zinc telluride
Cadmium zinc telluride, or CZT, is a compound of cadmium, zinc and tellurium or, more strictly speaking, an alloy of cadmium telluride and zinc telluride. A direct bandgap semiconductor, it is used in a variety of applications, including radiation detectors, photorefractive gratings,...

 is formed which is used in solid-state X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 detectors.

Alloyed with both cadmium and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, to form mercury cadmium telluride, an infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 sensitive semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 material is formed. Organotellurium compounds such as dimethyl telluride, diethyl telluride, diisopropyl telluride, diallyl telluride and methyl allyl telluride are used as precursors for metalorganic vapor phase epitaxy growth of II-VI compound semiconductor
Compound semiconductor
A compound semiconductor is a semiconductor compound composed of elements from two or more different groups of the periodic table . These semiconductors typically form in groups 13-16 ,...

s. Diisopropyl telluride (DIPTe) is employed as the preferred precursor for achieving the low-temperature growth of CdHgTe by MOVPE. For these processes highest purity metalorganics
Metalorganics
Metalorganic compounds are a class of chemical compounds that contain metals and organic ligands. Metalorganic compounds are used extensively in materials science in applications such as metalorganic vapour phase epitaxy or sol-gel processing using alkoxides...

 of both selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 and tellurium are used. The compounds for semiconductor industry and are prepared by adduct purification
Adduct purification
Adduct purification is a technique for preparing extremely pure simple organometallic compounds, which are generally unstable and hard to handle, by purifying a stable adduct with a Lewis acid and then obtaining the desired product from the pure adduct by thermal decomposition.Epichem Limited is...

.

Tellurium as a tellurium suboxide is used in the media layer of several types of rewritable optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...

s, including ReWritable Compact Discs
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

 (CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

), ReWritable Digital Video Discs (DVD-RW
DVD-RW
A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The smaller Mini DVD-RW holds 1.46 GB, with a diameter of 8 cm.The primary advantage of DVD-RW over...

) and ReWritable Blu-ray Disc
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...

s.

Tellurium is used in the new phase change memory chips. developed by Intel. Bismuth telluride
Bismuth telluride
Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which, when alloyed with antimony or selenium is an efficient thermoelectric material for refrigeration or portable power generation...

 (Bi2Te3) and lead telluride are working elements of thermoelectric devices. Lead telluride is used in far-infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 detectors.

Other uses

  • Used to color ceramic
    Ceramic
    A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

    s.
  • The strong increase in optical refraction upon the addition of selenides and tellurides into glass is used in the production of glass fibers for telecommunications. These chalcogenide glass
    Chalcogenide glass
    A chalcogenide glass is a glass containing one or more chalcogenide elements. These are Group 16 in the periodic table e.g. sulfur, selenium or tellurium. Such glasses are covalently bonded materials and may be classified as network solids. In effect, the entire glass matrix acts like an...

    es are widely used.
  • Mixtures of selenium and tellurium are used with barium peroxide
    Barium peroxide
    Barium peroxide is the chemical compound with the formula BaO2. This grey-white solid is one of the most common inorganic peroxides. Barium peroxide is an oxidizing agent, which is used for bleaching...

     as oxidizer in the delay powder of electric blasting cap
    Blasting cap
    A blasting cap is a small sensitive primary explosive device generally used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive....

    s.
  • Organic tellurides have been employed as initiators for living radical polymerization and electron-rich mono- and di-tellurides possess antioxidant
    Antioxidant
    An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

     activity.
  • Rubber can be vulcanized with tellurium instead of sulfur or selenium. The rubber produced in this way shows improved heat resistance.
  • Tellurite
    Tellurite
    Tellurite is a rare oxide mineral composed of tellurium dioxide .It occurs as prismatic to acicular transparent yellow to white orthorhombic crystals. It occurs in the oxidation zone of mineral deposits in association with native tellurium, emmonsite and other tellurium minerals. Its name comes...

     agar
    Agar
    Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...

     is used to identify member of the corynebacterium
    Corynebacterium
    Corynebacterium is a genus of Gram-positive rod-shaped bacteria. They are widely distributed in nature and are mostly innocuous. Some are useful in industrial settings such as C. glutamicum. Others can cause human disease. C...

     genus, most typically Corynebacterium diphtheriae
    Corynebacterium diphtheriae
    Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria. It is also known as the Klebs-Löffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs and Friedrich Löffler .-Classification:Four subspecies are recognized: C. diphtheriae mitis, C....

    , the pathogen responsible for diphtheria
    Diphtheria
    Diphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. It is characterized by sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity...

    .

Biological role


Tellurium has no known biological function, although fungi can incorporate it in place of sulfur and selenium into amino acids such as telluro-cysteine and telluro-methionine. Organisms have shown a highly variable tolerance to tellurium compounds. Most organisms metabolize tellurium partly to form dimethyl telluride although dimethyl ditelluride is also formed by some species. Dimethyl telluride has been observed in hot springs at very low concentrations.

Precautions


Tellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare.
Tellurium is not reported to be carcinogenic.

Humans exposed to as little as 0.01 mg/m3 or less in air develop "tellurium breath", which has a garlic
Garlic
Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...

-like odor.
The garlic odor that is associated with human intake of tellurium compounds is caused from the tellurium being metabolized by the body. When the body metabolizes tellurium in any oxidation state, the tellurium is converted into dimethyl telluride, (CH3)2Te, which is volatile and is the cause of the garlic-like smell. Even though the metabolic pathways of tellurium are not known, it is generally assumed that they resemble those of the more extensively studied selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

, because the final methylated metabolic products of the two elements are similar.

External links