Tellurium Facts – Element Te or Atomic Number 52

Tellurium Facts

Tellurium is a chemical element with the symbol Te and atomic number 52. It is a rare, brittle, mildly toxic metalloid with properties in common with sulfur and selenium. It is best known for its use in solar cells and the garlic odor it gives the breath of a person exposed to it.

Tellurium Discovery, Naming, and Isolation

Tellurium was discovered in ore from a gold mine in Transylvania (now part of Romania) in 1782 by Franz-Joseph Müller von Reichenstein, a mining engineer and mineralogist. Initially, he did not recognize the substance as a new element. However, the new material had properties he had not encountered, such as the radish-like odor it produced then heated and the red color it gave to sulfuric acid. He called the metal aurum paradoxum (paradoxical gold) and metallum problematicum (problem metal).

In 1798, Germ chemist Martin Klaproth identified the substance as a new element. Klaproth gave it the name “tellurium,” derived from the Latin word “tellus,” meaning earth.

Allotropes, Appearance, and Properties

There are two tellurium allotropes. Crystalline tellurium is silvery-white in color and has a metallic luster and hexagonal crystal form. Exposure to air darkens the silver. The crystal form is brittle and easily broken. The gray amorphous allotrope brownish-black in color and typically forms as a precipitate in chemical reactions.

Tellurium is a semiconductor with a higher electrical conductivity in certain directions, which increases slightly when exposed to light. It has a melting point of 449.51 °C and a boiling point of 988 °C, which are the highest for the chalcogens. Its density is about 6.24 grams per cubic centimeter at room temperature.

Electron Levels of a Tellurium Atom

Element Group: Chalcogens

As a member of the chalcogens, tellurium exhibits a -2 oxidation state, but the +2, +4, and +6 states are also common. Like its neighbors selenium and sulfur, it forms various compounds, including oxides, halides, and acids.

Natural and Synthetic Isotopes

Natural tellurium consists of eight natural isotopes, with 130Te and 128Te being the most abundant. Six isotopes are stable (120Te, 122Te, 123Te, 124Te, 125Te, 126Te), while the other two are mildly radioactive and have very long half-lives (128Te and 130Te). There are over 30 unstable synthetic isotopes, which form in nuclear reactors or particle accelerators.

Abundance and Sources

Neutron star collisions are one process that forms tellurium. Tellurium is one of the rarest stable solid elements in the Earth’s crust, with an abundance of about 1 microgram per kilogram. This abundance is comparable to that of platinum. Tellurium sometimes occurs in its native or elemental form, but more commonly occurs in minerals associated with gold, such as calaverite and krennerite, or in copper ores.

For most countries, tellurium is a by-product of other mining processes. However, China mines tellurium as a target element. The lead producers of the metalloid are China, Russia, Japan, Canada, Uzbekistan, and Sweden.


The purification of tellurium involves roasting mineral ores to convert tellurides to oxides, followed by reduction to metallic tellurium. Further purification by zone refining or electrolytic methods yield high-purity tellurium for industrial applications.

Uses of Tellurium

The main uses of tellurium are for thin-film solar cells, thermoelectrics, metallurgy, and rubber production:

  • Alloys: It improves the machinability of copper and stainless steel.
  • Semiconductors: Cadmium telluride (CdTe) is a key material in the production of thermoelectric devices and solar cells. CdTe converts temperature differences into electrical energy.
  • Rubber: The element is a vulcanizing agent that increases the durability of rubber.
  • Isotope Production: Neutron bombardment of tellurium produces iodine-131, which finds use in hydraulic fracturing and as a thyroid condition treatment.
  • Optics: Tellurides increase the optical refraction of glass, mainly for fiberoptics applications.
  • Oxidizer: Selenium and tellurium, together with barium peroxide, form an oxidizer for electric blasting caps.
  • Pigments: Tellurium compounds form pigments for ceramics and decolorizing glass.

Biological Role, Health Effects, and Toxicity

Tellurium has no known biological role in humans and is mildly toxic. It is likely not carcinogenic. Inhalation or ingestion of tellurium compounds leads to ‘tellurium breath’, which has a garlic-like odor. This odor persists at least eight months following exposure. The element accumulates, potentially causing drowsiness, nausea, and in extreme cases, neurological effects.

Fungi and many bacteria incorporate tellurium in place of selenium and sulfur in amino acids.

Table of Key Tellurium Facts for Scientists

Atomic Number52
Atomic Weight127.60
Group16 (Chalcogens)
Electron Configuration[Kr] 4d10 5s2 5p4
Electrons per Shell2, 8, 18, 18, 6
State of MatterSolid
Melting Point449.51 °C
Boiling Point988 °C
Density6.24 g/cm³
Heat of Fusion17.49 kJ/mol
Heat of Vaporization114.1 kJ/mol
Molar Heat Capacity25.73 J/(mol·K)
Oxidation States-2, -1, 0, +1, +2, +3, +4, +5, +6
Electronegativity2.1 (Pauling scale)
Ionization Energies869.3, 1790, 2698 kJ/mol
Atomic Radius140 pm
Covalent Radius138 pm
Van der Waals Radius206 pm
Crystal StructureHexagonal
Thermal Conductivity1.97-3.38 W/(m·K)
Electrical Resistivity~1 x 105 µΩ·m at 25 °C
Magnetic OrderingDiamagnetic
Young’s Modulus43 GPa
Shear Modulus16 GPa
Mohs Hardness2.25

Interesting Tellurium Facts

Here are some additional unusual and interesting tellurium facts:

  • At the beginning of the 1893 gold rush, miners discarded a material that looked like pyrite (Fool’s Gold) and used it to fill in potholes. Later, they discovered it was actually gold telluride (AuTe2) and rushed to mine the streets for the mineral.
  • In the 1920s, Thomas Midgley Jr. discovered that tellurium was an effective additive for preventing engine knock. However, it produced an unpleasant odor, so Midgley decided a better additive was tetraethyl lead.
  • Tellurium is more abundant in the cosmos than it is on Earth. One theory is that tellurium (and selenium) formed hydrides that evaporated and escaped.
  • The element has interesting acoustic properties, acting as acoustic semiconductors.
  • Asteroids and some meteorites contain higher levels of the element than occur in the Earth’s crust, making them potential mining sources.


  • Emsley, John (2003). Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-850340-8.
  • Knockaert, Guy (2000). “Tellurium and Tellurium Compounds”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. ISBN 978-3527306732. doi:10.1002/14356007.a26_177
  • Ramadan, Shadia E.; Razak, A. A.; Ragab, A. M.; El-Meleigy, M. (1989). “Incorporation of tellurium into amino acids and proteins in a tellurium-tolerant fungi”. Biological Trace Element Research. 20 (3): 225–32. doi:10.1007/BF02917437
  • von Reichenstein, F. J. M. (1783). “Versuche mit dem in der Grube Mariahilf in dem Gebirge Fazebay bey Zalathna vorkommenden vermeinten gediegenen Spiesglaskönig” [Experiments with supposedly native antimony occurring in the Mariahilf mine in the Fazeby mountains near Zalathna]. Physikalische Arbeiten der Einträchtigen Freunde in Wien. 1783 (1.Quartal): 63–69.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.