Tellurium

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antimony ← tellurium → iodine
Se
↑
Te
↓
Po
Appearance
silvery lustrous gray
General properties
Name, symbol, number tellurium, Te, 52
Element category metalloid
Group, period, block 16, 5, p
Standard atomic weight 127.60 g·mol−1
Electron configuration [Kr] 5s2 4d10 5p4
Electrons per shell 2, 8, 18, 18, 6 (Image)
Physical properties
Phase solid
Density (near r.t.) 6.24 g·cm−3
Liquid density at m.p. 5.70 g·cm−3
Melting point 722.66 K, 449.51 °C, 841.12 °F
Boiling point 1261 K, 988 °C, 1810 °F
Heat of fusion 17.49 kJ·mol−1
Heat of vaporization 114.1 kJ·mol−1
Specific heat capacity (25 °C) 25.73 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K     (775) (888) 1042 1266
Atomic properties
Oxidation states 6, 5, 4, 2, -2
(mildly acidic oxide)
Electronegativity 2.1 (Pauling scale)
Ionization energies 1st: 869.3 kJ·mol−1
2nd: 1790 kJ·mol−1
3rd: 2698 kJ·mol−1
Atomic radius 140 pm
Covalent radius 138±4 pm
Van der Waals radius 206 pm
Miscellanea
Crystal structure hexagonal
Magnetic ordering diamagnetic[1]
Thermal conductivity (300 K) (1.97–3.38) W·m−1·K−1
Speed of sound (thin rod) (20 °C) 2610 m/s
Young's modulus 43 GPa
Shear modulus 16 GPa
Bulk modulus 65 GPa
Mohs hardness 2.25
Brinell hardness 180 MPa
CAS registry number 13494-80-9
Most stable isotopes
Main article: Isotopes of tellurium
iso NA half-life DM DE (MeV) DP
120Te 0.09% >2.2×1016y ε ε 1.701 120Sn
121Te syn 16.78 d ε 1.040 121Sb
122Te 2.55% 122Te is stable with 70 neutrons
123Te 0.89% >1.0×1013 y ε 0.051 123Sb
124Te 4.74% 124Te is stable with 72 neutrons
125Te 7.07% 125Te is stable with 73 neutrons
126Te 18.84% 126Te is stable with 74 neutrons
127Te syn 9.35 h β− 0.698 127I
128Te 31.74% 2.2×1024 y β−β− 0.867 128Xe
129Te syn 69.6 min β− 1.498 129I
130Te 34.08% 7.9×1020 y β−β− 2.528 130Xe
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Tellurium (pronounced /tɪˈlʊəriəm, tɛ-/ te-LOOR-ee-əm) is a chemical element that has the symbol Te and atomic number 52. A brittle, mildly toxic, silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. Tellurium is primarily used in alloys and as a semiconductor.

Contents

[edit] Characteristics

Tellurium belongs to the same chemical family as oxygen, sulfur, selenium, and polonium: the chalcogen family.

When crystalline, 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 (Te(OH)6). However, there is some debate whether this form is really amorphous or made of minute crystals.

[edit] Compounds

See also: Category:Tellurium compounds

Tellurium is in the same group as sulfur and selenium and forms similar compounds. It exhibits the oxidation states −2, +2, +4, and +6, with the +4 state being most common.[2]

[edit] Tellurides

The −2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, ZnTe, formed by heating tellurium with zinc.[3] Decomposition of ZnTe with hydrochloric acid yields hydrogen telluride, H2Te, the tellurium analogue of the other chalcogen hydrides, H2O, H2S, and H2Se:

ZnTe + 2 HCl → ZnCl2 + H2Te

H2Te reacts with many metals to form tellurides, containing the Te2− anion.[3] Gold and silver tellurides are considered good ores.

[edit] Halogen compounds

The +2 oxidation state is exhibited by the monoxide, TeO, and the dihalides, TeCl2, TeBr2, and TeI2. The dihalides have not been obtained in pure form,[4]:274 although they are known decomposition products of the tetrahalides in organic solvents, and their derived tetrahalotellurates are well-characterized:

Te + X2 + 2 X− → TeX2−4

where X is Cl, Br, or I. These anions are square planar in geometry.[4]:281 Polynuclear anionic species also exist, such as the dark brown Te2I2−6,[4]:283 and the black Te4I2−14.[4]:285

Fluorine forms two halides with tellurium: the mixed-valence Te2F4, and TeF6. In the +6 oxidation state, the –OTeF5 structural group occurs in a number of compounds such as HOTeF5, B(OTeF5)3, Xe(OTeF5)2, Te(OTeF5)4, and Te(OTeF5)6.[5] The square antiprismic anion TeF2−8 is also attested.[6] The other halogens do not form halides with tellurium in the +6 oxidation state, but only tetrahalides (TeCl4, TeBr4, and TeI4) in the +4 state, and other lower halides (Te3Cl2, Te2Cl2, Te2Br2, Te2I, and two forms of TeI). In the +4 oxidation state, halotellurate anions are known, such as TeCl2−6 and Te2Cl2−10. Halotellurium cations are also attested, inculding TeI+3, found in TeI3AsF6.[7]

[edit] Oxygen compounds

Tellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of TeSO3 in vacuum, disproportionating into tellurium dioxide, TeO2, and elemental tellurium upon heating.[8][9] 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.[10]

Tellurium dioxide is formed by heating tellurium in air, causing it to burn with a blue flame.[3] Tellurium trioxide, β-TeO3, is obtained by thermal decomposition of Te(OH)6. 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 Te4+, OH−, and O−2.[11] Tellurium also exhibits mixed-valence oxides, Te2O5 and Te4O9.[11]

The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid (H2TeO3), orthotelluric acid (Te(OH)6), and metatelluric acid ((H2TeO4)n).[10] The two forms of telluric acid form tellurate salts containing the TeO2−4 and TeO6−6 anions, respectively. Tellurous acid forms tellurite salts containing the anion TeO2−3. Other tellurium cations include TeF2+8, which consists of two fused tellurium rings, and the polymeric TeF2+7.

[edit] Zintl cations

When tellurium is treated with concentrated sulfuric acid, it forms red solutions containing the Zintl ion, Te2+4. The oxidation of tellurium by AsF5 in liquid SO2 also produces this square planar cation, as well as with the trigonal prismatic, yellow-orange Te4+6:[6]

4 Te + 3 AsF5 → Te2+4(AsF−6)2 + AsF3
6 Te + 6 AsF5 → Te4+6(AsF−6)4 + 2 AsF3

Other tellurium Zintl cations include the polymeric Te2+7, and the blue-black Te2+8, which consists of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride:[6]

8 Te + 2 WCl6 → Te2+8(WCl−6)2

Interchalcogen cations also exist, such as Te2Se2+6 (distorted cubic geometry) and Te2Se2+8. These are formed by oxidising mixtures of tellurium and selenium with AsF5 or SbF5.[6]

[edit] Organic compounds

In organic chemistry, tellurium forms analogues of alcohols and thiols, having the functional group –TeH, called tellurols. The –TeH functional group is also referred to with the prefix tellanyl-.

[edit] Isotopes

Main article: isotopes of tellurium

There are 30 known isotopes of tellurium with atomic masses that range from 108 to 137. Naturally found tellurium consists of eight isotopes (listed in the main article); three of them are observed to be radioactive. 128Te has the longest known half-life, 2.2×1024 years[12], among all radioisotopes.[13] Tellurium is the lightest element known to undergo alpha decay, with isotopes 106Te to 110Te being able to undergo this mode of decay.

[edit] History

Tellurium (Latin tellus meaning "earth") was discovered in 1782 by the Hungarian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Nagyszeben (now, Sibiu) Transylvania. In 1789, another Hungarian scientist, Pál Kitaibel, also discovered the element independently, but later he gave the credit to Müller. In 1798, it was named by Martin Heinrich Klaproth who earlier isolated it from the mineral calaverite.[14]

Tellurium was used as a chemical bonder in the making of the outer shell of the first atom bomb. The 1960s brought growth in thermoelectric applications for tellurium, as well as its use in free-machining steel, which became the dominant use.

[edit] Occurrence

See also: category:Telluride minerals and Telluride, Colorado
Tellurium on quartz (Moctezuma, Sonora, Mexico)

With an abundance in the Earth's crust comparable to that of platinum, tellurium is one of the rarest stable solid element in the Earth's crust. Its abundance is about 1 µg/kg.[15] By comparison, even the rarest of the lanthanides have crustal abundances of 500 µg/kg (see Abundance of elements in Earth's crust).

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, even though rubidium is ten thousand times more abundant in the Earth's crust. The extraordinarily low abundance of tellurium on Earth is because during the Earth's formation, the stable form of elements in the absence of oxygen and water was controlled by the oxidation and reduction of hydrogen. Under this scenario elements such as tellurium which form volatile hydrides were severely depleted during the formation of the Earth's crust through evaporation. Tellurium and selenium are the heavy elements mostly depleted in the Earth's crust by this process.[citation needed]

Tellurium is sometimes found in its native (elemental) form, but is more often found as the tellurides of gold (calaverite, krennerite, petzite, sylvanite, and others). Tellurium compounds are the most common chemical compounds of gold found in nature (rare non-tellurides such as gold aurostibite and bismuthide are known). Tellurium is also found combined with elements other than gold, in salts of other metals. The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. It is a component of dusts from blast furnace refining of lead. Treatment of 500 tons of copper ore typically yields one pound (0.45 kg) of tellurium. Tellurium is produced mainly in the United States, Canada, Peru, and Japan.

Commercial-grade tellurium is usually marketed as minus 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The year-end price for tellurium in 2000 was US$14 per pound. In recent years, tellurium price was driven up by increased demand and limited supply, reaching as high as US$100 per pound in 2006.[16][17]

[edit] Applications

Tellurium is a p-type semiconductor that shows a greater conductivity in certain directions which depends on atomic alignment. Chemically related to selenium and sulfur, the conductivity of this element increases slightly when exposed to light (photoconductivity).

It can be doped with copper, gold, silver, tin, or other metals. When in its molten state, tellurium is corrosive to copper, iron, and stainless steel.

Tellurium gives a greenish-blue flame when burned in normal air and forms tellurium dioxide as a result.

Metal alloys: [18]

  • It is mostly used in alloys with other metals. It is added to lead to improve its strength and durability, and to decrease the corrosive action of sulfuric acid.
  • When added to stainless steel and copper it makes these metals more workable. It is alloyed into cast iron for chill control.

Other uses:

High purity metalorganics of both selenium and tellurium are used in the semiconductor industry, and are prepared by adduct purification.[19][20]

Semiconductor and electronic industry uses:

  • Tellurium is used in cadmium telluride (CdTe) solar panels. NREL lab tests using this material achieved some of the highest efficiencies for solar cell electric power generation. First Solar started massive commercial production of CdTe solar panels in recent years, significantly increased tellurium demand. If some of the cadmium in CdTe is replaced by zinc then CdZnTe is formed which is used in solid-state x-ray detectors.

[edit] Precautions

Tellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare.[25] Tellurium is not reported to be carcinogenic.[25]

Humans exposed to as little as 0.01 mg/m3 or less in air develop "tellurium breath", which has a garlic-like odor.[26] 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 gets 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, because the final methylated metabolic products of the two elements are similar.

[edit] References

  1. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81th edition, CRC press.
  2. ^ G. W. Leddicotte (1961), The radiochemistry of tellurium, Nuclear science series, Subcommittee on Radiochemistry, National Academy of Sciences-National Research Council, p. 5 
  3. ^ a b c Henry Enfield Roscoe; Carl Schorlemmer (1878). A treatise on chemistry. 1. Appleton. pp. 367-368. 
  4. ^ a b c d H. J. Emeleus (1990). A. G. Sykes. ed. Advances in Inorganic Chemistry. 35. Academic Press. ISBN 0120236354. 
  5. ^ John H. Holloway; David Laycock (1983). "Preparations and Reactions of Inorganic Main-Group Oxide-Fluorides". in Harry Julius Emeléus, A. G. Sharpe. Advances in inorganic chemistry and radiochemistry. Serial Publication Series. 27. Academic Press. p. 174. ISBN 0120236273. 
  6. ^ a b c d Egon Wiberg; Arnold Frederick Holleman (2001). Nils Wiberg. ed. Inorganic chemistry. Academic Press. p. 588. ISBN 0123526515. 
  7. ^ Zhengtao Xu (2007), "Recent developments in binary halogen-chalcogen compounds, polyanions and polycations", in Francesco A. Devillanova, Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium, Royal Society of Chemistry, pp. 457-466, ISBN 0854043667 
  8. ^ Mel M. Schwartz (2002). "Tellurium". Encyclopedia of materials, parts, and finishes (2nd ed.). CRC Press. ISBN 1566766613. 
  9. ^ Edward Divers; M. Shimosé (1883). "On a new oxide of tellurium". Journal of the Chemical Society (Royal Society of Chemistry (Great Britain)) 43. 
  10. ^ a b "The Oxides and Oxyacids of Tellurium". Chemical Reviews 66 (6): 657–675. December 1966. doi:10.1021/cr60244a003.  edit
  11. ^ a b Mathias S. Wickleder (2007). "Chalcogen-Oxygen Chemistry". in Francesco A. Devillanova. Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium. Royal Society of Chemistry. p. 348-350. ISBN 0854043667. 
  12. ^ "WWW Table of Radioactive Isotopes: Tellurium". Nuclear Science Division, Lawrence Berkeley National Laboratory. 2008. http://ie.lbl.gov/toi/nuclide.asp?iZA=520128. 
  13. ^ "Noble Gas Research". Laboratory for Space Sciences, Washington University in St. Louis. 2008. http://presolar.wustl.edu/work/noblegas.html#tellurium. 
  14. ^ Diemann, Ekkehard; Müller, Achim; Barbu, Horia (2002). "Die spannende Entdeckungsgeschichte des Tellurs (1782 - 1798) Bedeutung und Komplexität von Elemententdeckungen". Chemie in unserer Zeit 36 (5): 334–337. doi:10.1002/1521-3781(200210)36:5<334::AID-CIUZ334>3.0.CO;2-1. 
  15. ^ Robert U. Ayres, Leslie Ayres (2002). A handbook of industrial ecology. Edward Elgar Publishing. p. 396. ISBN 1840645067. http://books.google.com/books?id=g1Kb-xizc1wC&pg=PA396. 
  16. ^ "An Arizona tellurium rush?". May 21, 2007. http://arizonageology.blogspot.com/2007/05/arizona-tellurium-rush.html. Retrieved 2009-08-08. 
  17. ^ "Byproducts Part I: Is There a Tellurium Rush in the Making?". April 19, 2007. http://www.resourceinvestor.com/News/2007/4/Pages/Byproducts-Part-I--Is-There-a-Tellurium-Rush-in.aspx. Retrieved 2009-08-08. 
  18. ^ George, Micheal W. (2007). "Mineral Yearbook 2007: Selenium and Tellurium". United States geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/selenium/myb1-2007-selen.pdf. 
  19. ^ "Ultra-pure organotellurium precursors for the low temperature MOVPE growth of II/VI compound semiconductors". Journal of Crystal Growth 93: 744–749. 1988. doi:10.1016/0022-0248(88)90613-6. 
  20. ^ Mullin, John B. et al. U.S. Patent 5,117,021 "Method for purification of tellurium and selenium alkyls", May 26, 1992
  21. ^ Farivar, Cyrus (2006-10-19). "Panasonic says that its 100GB Blu-ray discs will last a century". http://www.engadget.com/2006/10/19/panasonic-says-that-its-100gb-blu-ray-discs-will-last-a-century/. Retrieved 2008-11-13. 
  22. ^ Kenichi Nishiuchi, Hideki Kitaura, Noboru Yamada and Nobuo Akahira (1998). "Dual-Layer Optical Disk with Te–O–Pd Phase-Change Film". Jpn. J. Appl. Phys. 37: 2163-2167. doi:10.1143/JJAP.37.2163. 
  23. ^ Hudgens, S.; Johnson, B. (2004). "Overview of Phase-Change Chalcogenide Nonvolatile Memory Technology". Material Research Society Bulletin 29 (11): 1–4. http://www.engr.sjsu.edu/sgleixner/mate270/LectureNotes/Hudgens_MRS.pdf. 
  24. ^ Geppert, Linda. "The New Indelible Memories". IEEE spectrum online. http://www.spectrum.ieee.org/print/1501. Retrieved 2009-02-08. 
  25. ^ a b Harrison, W; S Bradberry, J Vale (1998-01-28). "Tellurium". International Programme on Chemical Safety. http://www.intox.org/databank/documents/chemical/tellur/ukpid84.htm. Retrieved 2007-01-12. 
  26. ^ Lide, D. R., ed. (2005), CRC Handbook of Chemistry and Physics (86th ed.), Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5 

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