Tellurium

52 antimony ← tellurium → iodine Se ↑ Te ↓ Po 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/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)
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
	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
Main article: Isotopes of tellurium iso NA half-life DM DE (MeV) DP 120Te 0.096% Te is stable with 68 neutrons 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 128Te 31.687% 2.2×1024 y β−β− 0.867 128Xe 130Te 33.799% 7.9×1020 y β−β− 2.528 130Xe

Tellurium (chemical symbol Te, atomic number 52) is a relatively rare chemical element that belongs to the group of metalloids—its chemical properties are intermediate between those of metals and nonmetals. Silvery in color, it looks like tin, but chemically it is more closely related to selenium and sulfur.

This element is primarily used in alloys. For instance, when added to lead, it enhances the metal's strength and durability; when alloyed with stainless steel and copper, it makes them more workable. When alloyed with both cadmium and mercury, it forms an infrared-sensitive semiconductor. In addition, it is used in ceramics, glasses, and blasting caps. Bismuth telluride is useful for thermoelectric devices, and cadmium telluride has potential applications in photovoltaic cells for solar power. When zinc is added to cadmium telluride, the product is extremely well-suited for use in solid-state detectors for X rays and gamma rays.

Yet, tellurium and its compounds should be considered toxic and need to be handled with care. Exposure to even small amounts of tellurium can generate a garlicky odor in one's breath, sweat, and urine. Additional symptoms of exposure to the element or its compounds (at relatively high concentrations) include headache, dyspnea, weakness, skin rash, a metallic taste in the mouth, and blue-black markings on the fingers, neck, face, and gums. Death may occur from pulmonary edema. A person exposed to tellurium compounds should be given medical attention.

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 if properly handled, 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 five, between antimony and iodine.

In its pure and crystalline state, tellurium has a silvery-white color and a metallic luster. When the element is precipitated from a solution of tellurous acid (H₂TeO₃) or telluric acid (H₆TeO₆), it appears to have an amorphous form. There is, however, some debate whether this form is really amorphous or composed of minute crystals.

Tellurium is brittle and can be easily pulverized. When burned in air, it produces a greenish-blue flame and forms tellurium dioxide. In its molten state, the element is corrosive toward copper, iron, and stainless steel.

Chemically, tellurium is related to sulfur and selenium and forms similar compounds. Yet, while sulfur and selenium are nonmetals, tellurium (as well as polonium) is classified as a metalloid.

Tellurium is a P-type semiconductor. Its conductivity, which is higher in certain directions, increases slightly on exposure to light. It can be doped with various metals, including tin, copper, silver, and gold.

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).

Compounds

Tellurium can form a variety of compounds. Some examples are given below.

• Bismuth(III) telluride (Bi₂Te₃): This compound is a semiconductor and an efficient thermoelectric material for devices used in refrigeration or portable power generation. Although generally a low-risk material, it can be fatal if large doses are ingested. One should avoid breathing its dust. Also, its reaction with water may release toxic fumes.

• Cadmium telluride (CdTe): This crystalline compound is a useful material for solar cells (photovoltaics). It is used as an infrared optical material for optical windows and lenses. It can be alloyed with mercury to make a versatile infrared detector material (HgCdTe). Alloyed with a small amount of zinc, it makes an excellent solid-state X-ray and gamma ray detector (CdZnTe).

• Silver telluride (Ag₂Te): It occurs in nature in the form of the minerals hessite and empressite. It is a semiconductor that can be doped to have either n-type or p-type conductivity. On heating, silver is lost from the material.

• Telluric acid (H₆TeO₆ or Te(OH)₆): It is a weak acid, forming tellurate salts with strong bases.^[1] In addition, it is an oxidizing agent. It can be formed by the oxidation of tellurium or tellurium dioxide with hydrogen peroxide or chromium trioxide.

• Tellurium dioxide (TeO₂ or paratellurite): This solid oxide is the main product of burning tellurium in air. It is highly insoluble in water and completely soluble in concentrated sulfuric acid. It is amphoteric, which means that it can act as an acid or as a base, depending on the solution it is in. It is used as an acousto-optic material. It is also a conditional glass former, meaning that it will form a glass with small additions of a second compound such as an oxide or halide. TeO₂ glasses have high refractive indices, transmit into the mid-infrared region of the electromagnetic spectrum, and have properties useful for optical fiber amplification.

• Tellurium hexafluoride (TeF₆): It is a colorless, highly toxic gas with a foul smell. It is most commonly prepared by passing fluorine gas over tellurium metal at 150 °C. Below this temperature, a mixture of lower fluorides are formed, including tellurium tetrafluoride and ditellurium decafluoride. The physical properties of tellurium hexafluoride resemble those of the sulfur analog, but unlike the latter, it is not chemically inert. It is hydrolyzed in water to form telluric acid, and it reacts with Te below 200 °C.

Applications

• Tellurium is mostly used in alloys with other metals. Consider some examples.
  • Alloyed with lead, it improves the material's strength and durability, and decreases the corrosive action of sulfuric acid.
  • When added to stainless steel or copper, it makes these metals more workable.
  • It is alloyed with cast iron for chill control.
  • When alloyed with both cadmium and mercury, it forms mercury cadmium telluride, an infrared-sensitive semiconductor.
• Tellurium is also used in ceramics and chalcogenide glasses.
• It is used in blasting caps.
• Bismuth telluride (Bi₂Te₃) is used in thermoelectric devices for refrigeration or portable power generation.
• 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. It is used as an infrared optical material for optical windows and lenses.
• If cadmium telluride is alloyed with some zinc to form CdZnTe, this material is used in solid-state detectors for X rays and gamma rays.

Precautions

Tellurium and its compounds should be considered toxic and need to be handled with care. A person exposed to as little as 0.01 milligrams (or less) of tellurium per cubic meter of air develops "tellurium breath," which has a garlicky odor. The same smell is also present in sweat and urine. The body metabolizes tellurium in any oxidation state, converting it to dimethyl telluride. This product is volatile and smells like garlic.

Exposure to tellurium or its compounds can also cause headache, dyspnea, weakness, skin rash, and a metallic taste in the mouth. In addition, it can produce bluish-black markings on the fingers, neck, face, and gums. Death may occur from pulmonary edema. People exposed to tellurium compounds should receive medical attention.

See also

• Chemical element
• Periodic table

Notes

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Tellurium Retrieved December 5, 2007.

External links

All links retrieved January 21, 2020.

• WebElements.com – Tellurium