Tellurium
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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/cm³ | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Liquid density at m.p. | 5.70 g/cm³ | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of vaporization | 114.1 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat capacity | (25 °C) 25.73 J/(mol·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
2nd: 1790 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
3rd: 2698 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound (thin rod) | (20 °C) 2610 m/s | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound (thin rod) | (r.t.) 43 m/s | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Shear modulus | 16 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bulk modulus | 65 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mohs hardness | 2.25 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Brinell hardness | 180 MPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
CAS registry number | 13494-80-9 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
Notable isotopes | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Tellurium (IPA: /tiˈlʊəriəm, tɛ-/) (chemical symbol Te, atomic number 52) is a relatively rare chemical element that is classified as a metalloid. Silver-white in color, it looks like tin. It is chemically related to selenium and sulfur. This element is primarily used in alloys and as a semiconductor.
Occurrence and production
In nature, tellurium is sometimes found in its elemental form, but it is more often found as the tellurides of gold and silver, such as the minerals calaverite, krennerite, petzite, and sylvanite. Tellurium compounds are the only chemical compounds of gold found in nature. Yet, unlike gold, tellurium itself is also found combined with other elements, forming metallic salts.
The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. In addition, it is a component of dusts from blast furnace refining of lead. Tellurium is produced mainly in the United States, Canada, Peru, and Japan.
Commercial-grade tellurium, which is not toxic, is usually marketed as minus 200-mesh powder, but it is also available as slabs, ingots, sticks, and lumps.
History
Tellurium (from the Latin word tellus, meaning "earth") was discovered in 1782 by the Hungarian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Transylvania. Another Hungarian scientist, Pál Kitaibel, discovered the element independently in 1789, but he later gave the credit to Müller. It was named in 1798 by Martin Heinrich Klaproth who had isolated it earlier.
The 1960s brought growth in thermoelectric applications for tellurium, as well as its use in free-machining steel, which became the dominant use.
Notable characteristics
In the periodic table, tellurium is located in group 16 (formerly group 6A), between selenium and polonium. Along with sulfur, selenium, and polonium, it is a member of the oxygen family of elements, also called the chalcogens. In addition, it lies in period 5, between antimony and iodine.
Tellurium is chemically related to sulfur and selenium and forms similar compounds. Yet, while sulfur and selenium are nonmetals, tellurium and polonium are classified as metalloids.
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. When burned in air, it produces a greenish-blue flame and forms tellurium dioxide as a result. In its molten state, tellurium is corrosive toward copper, iron, and stainless steel.
Isotopes
There are 30 known isotopes of tellurium, with atomic masses ranging from 108 to 137. Naturally occurring tellurium consists of eight isotopes (listed in the table on the right), three of which are radioactive. Among all its radioactive isotopes, 128Te has the longest half-life (2.2×1024 years).
Applications
- Tellurium is mostly used in alloys with other metals. For example, 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 with cast iron for chill control.
- It is used in ceramics.
- It is also used in chalcogenide glasses.
- Tellurium is also used in blasting caps.
- Bismuth telluride (Bi2Te3) is used in thermoelectric devices.
- Cadmium telluride (CdTe) has potential applications in 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.
- When alloyed with both cadmium and mercury, it forms mercury cadmium telluride, an infrared-sensitive semiconductor.
<>Organic tellurides have been employed as initiators for living radical polymerisation and electron-rich mono- and di-tellurides possess antioxidant activity.
Compounds
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A compound with metal or hydrogen and similar ions is called a telluride. Good ores of tellurium consist of gold and silver tellurides. Compounds with tellurate ions (TeO42- or TeO66-) are known as tellurates.
See also Cadmium zinc telluride (CdZnTe), Telluric acid (H6TeO6).
- See also
- Category:Tellurium compounds
Precautions
Tellurium and its compounds should be considered to be toxic and need to be handled with care. A human exposed to as little as 0.01 milligram (or less) of tellurium per cubic meter of air develops "tellurium breath," which has a garlic-like odor. The body metabolizes tellurium in any oxidation state, converting it to dimethyl telluride. This product is volatile and produces the garlic-like smell.
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