Tellurium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements

52 antimony ← tellurium → iodine Se ↑ Te ↓ Po Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	tellurium, Te, 52
Chemical series	metalloids
Group, Period, Block	16, 5, p
Appearance	silvery lustrous gray
Atomic mass	127.60 (3) g/mol
Electron configuration	[Kr] 4d10 5s2 5p4
Electrons per shell	2, 8, 18, 18, 6
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
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
Crystal structure	hexagonal
Oxidation states	±2, 4, 6 (mildly acidic oxide)
Electronegativity	2.1 (Pauling scale)
Ionization energies ( more)	1st: 869.3 kJ·mol−1
	2nd: 1790 kJ·mol−1
	3rd: 2698 kJ·mol−1
Atomic radius	140 pm
Atomic radius (calc.)	123 pm
Covalent radius	135 pm
Van der Waals radius	206 pm
Miscellaneous
Magnetic ordering	nonmagnetic
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
Selected isotopes
Main article: Isotopes of tellurium iso NA half-life DM DE ( MeV) DP 120Te 0.096% >2.2×1016 y ε ε 1.701 120Sn 121Te syn 16.78 d ε 1.040 121Sb 122Te 2.603% Te is stable with 70 neutrons 123Te 0.908% >1.0×1013 y ε 0.051 123Sb 124Te 4.816% Te is stable with 72 neutrons 125Te 7.139% Te is stable with 73 neutrons 126Te 18.952% Te is stable with 74 neutrons 127Te syn 9.35 h β- 0.698 127I 128Te 31.687% 2.2×1024 y β−β− 0.867 128Xe 129Te syn 69.6 min β- 1.498 129I 130Te 33.799% 7.9×1020 y β−β− 2.528 130Xe
References

Tellurium ( IPA: /tiˈlʊəriəm, tɛ-/) is a chemical element in the periodic table that has the symbol Te and atomic number 52. A brittle silver-white metalloid which looks like tin, tellurium is chemically related to selenium and sulfur. This element is primarily used in alloys and as a semiconductor.

Notable characteristics

Tellurium crystal

Tellurium is a relatively rare element, in the same chemical family as oxygen, sulfur, selenium, and polonium (the chalcogens).

When crystalline, tellurium is silvery-white and when it is in its pure state it has a metallic luster. This 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. 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. It can be doped with copper, gold, silver, tin, or other metals. Tellurium gives a greenish-blue flame when burned in normal air and forms tellurium dioxide as a result. When in its molten state, tellurium is corrosive to copper, iron, and stainless steel.

Applications

It is mostly used in alloys with other metals. It is added to lead to improve its strength, durability and to decrease the corrosive action of sulfuric acid. When added to stainless steel and copper it makes these metals more workable. Other uses:

• It is alloyed into cast iron for chill control.
• Used in ceramics.
• It is used in chalcogenide glasses.
• Bismuth telluride (Bi₂Te₃) has found use in thermoelectric devices.

Tellurium is also used in blasting caps, and has potential applications in cadmium telluride (CdTe) solar panels. Some of the highest efficiencies for solar cell electric power generation have been obtained by using this material, but this application has not yet caused demand to increase significantly. If some of the cadmium in CdTe is replaced by zinc then CdZnTe is formed which is used in solid-state x-ray detectors.

Alloyed with both cadmium and mercury, to form mercury cadmium telluride, an infrared sensitive semiconductor material is formed. Organotellurium compounds such as dimethyl telluride, diethyl telluride, diisopropyl telluride, diallyl telluride and methyl allyl telluride are used as precursors for MOVPE growth of II-VI compound semiconductors. Diisopropyl telluride (DIPTe) is employed as the preferred precursor for achieving the low temperature growth of CdHgTe by MOVPE. High purity metalorganics of both selenium and tellurium are reported to be obtained by using innovative chemical purification strategy, also called adduct purification.

Organic tellurides have also been employed as initiators for living radical polymerisation and electron-rich mono- and di-tellurides possess antioxidant activity.

History

Tellurium (Latin tellus meaning "earth") was discovered in 1782 by the Romanian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Sibiu, Romania. 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.

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.

Occurrence

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 only chemical compounds of gold found in nature, but tellurium itself (unlike gold) is also found combined with other elements (in metallic salts). 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. Tellurium is produced mainly in the US, 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.

Compounds

Tellurium is in the same series as sulfur and selenium and forms similar compounds. A compound with metal or hydrogen and similar ions is called a telluride. Gold and silver tellurides are considered good ores. Compounds with tellurate ions complexes TeO₄^2- or TeO₆^6- are known as tellurates.

Isotopes

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 table to the right); three of them are observed to be radioactive. ¹²⁸Te has the longest known half-life, 2.2×10²⁴ years, among all radioactive isotopes. Tellurium is the first element which can undergo Alpha Decay, with isotopes ¹⁰⁶Te to ¹¹⁰Te being able to undergo this mode of decay.

Precautions

Humans exposed to as little as 0.01 mg/m³ or less in air develop "tellurium breath", which has a garlic-like odor. The garlic odour 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. Dimethyl telluride is volatile and produces the garlic-like smell.

Tellurium and tellurium compounds should be considered to be toxic and need to be handled with care.