2007 Schools Wikipedia Selection. Related subjects: Chemical elements
|Name, Symbol, Number||tellurium, Te, 52|
|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|
|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|
|Oxidation states||±2, 4, 6
(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|
|Atomic radius (calc.)||123 pm|
|Covalent radius||135 pm|
|Van der Waals radius||206 pm|
|Thermal conductivity||(300 K)
|Speed of sound (thin rod)||(20 °C) 2610 m/s|
|Young's modulus||43 GPa|
|Shear modulus||16 GPa|
|Bulk modulus||65 GPa|
|Brinell hardness||180 MPa|
|CAS registry number||13494-80-9|
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.
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.
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.
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.
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.
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 TeO42- or TeO66- are known as tellurates.
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.
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.