Tellurium (Te)

The ground-state configuration is [Kr] 4d¹⁰ 5s² 5p⁴. As a Group 16 (chalcogen) element, Te has six valence electrons (\(5s^2 5p^4\)), enabling oxidation states from −2 to +6 and rich p-block chemistry.

Tellurium commonly shows −2 (tellurides, e.g., \(\mathrm{Na_2Te}\)), +4 (tellurites) and +6 (tellurates):

• Tellurite: \(\mathrm{TeO_3^{2-}}\)
• Tellurate: \(\mathrm{TeO_4^{2-}}\)

Acid–base equilibria feature polyoxo species depending on pH and concentration.

Te-based alloys (e.g., Bi₂Te₃, PbTe, SnTe) exhibit high thermoelectric performance. The efficiency is gauged by the dimensionless figure of merit:

where \(S\) is Seebeck coefficient, \(\sigma\) electrical conductivity, \(\kappa\) thermal conductivity, and \(T\) absolute temperature. Te helps achieve large \(S\) and low \(\kappa\) via heavy atoms and complex bonding.

Cadmium telluride (CdTe) is a direct-band-gap semiconductor used in thin-film photovoltaics. It enables high absorption with micrometer-scale layers and can be deposited over large areas at comparatively low cost. Typical device stacks include transparent conductive oxides, CdS buffer, CdTe absorber, and back contacts.

Down the group (S → Se → Te):

• Metallic character increases (Te is a metalloid; S is a nonmetal).
• Bonding shifts toward more covalent/metallic behavior; heavier atoms favor lower electronegativity and larger, more polarizable orbitals.
• Heavier congeners (Te) more readily access +4/+6 oxo states and form heavier chalcogenides with metals.

In the body, some Te compounds are methylated to dimethyl telluride, \(\mathrm{(CH_3)_2Te}\), a volatile species exhaled through the lungs and excreted through sweat, producing a characteristic garlic odor even at low exposure.

Te is relatively rare in Earth’s crust and is found in telluride minerals (e.g., calaverite, \(\mathrm{AuTe_2}\)) and as a by-product in copper refining (anode slimes). Industrial recovery uses oxidative leaching of slimes to oxoanions (tellurite/tellurate), followed by selective precipitation and reduction to the element.

Important uses include:

• Thermoelectric modules (Bi₂Te₃, PbTe).
• Free-machining steels (Te additions improve chip-breaking).
• Phase-change memory & optical media using Ge–Sb–Te alloys (e.g., GST).
• Vulcanization & rubber curing aids and certain chemical catalysts.

Tellurium is a metalloid and an intrinsic p-type semiconductor in its trigonal form due to helical chains and anisotropic bonding. Its conductivity increases with temperature (semiconducting behavior) and can be tuned via alloying/doping in functional materials.

Many Te compounds are toxic. Good practice includes:

• Using fume hoods and avoiding dust/aerosols.
• Wearing gloves and eye protection.
• Minimizing skin contact and promptly cleaning spills.
• Managing wastes as hazardous materials.

Early signs of exposure can include a garlic-like breath/sweat odor due to \(\mathrm{(CH_3)_2Te}\).

Tellurium(IV) oxide is amphoteric and dissolves in strong base to give tellurite:

Under more oxidizing conditions, Te(VI) tellurate can form: