Tellurium is a soft (MH 2.25) and brittle semi-metallic element. It is commonly regarded as a metalloid, or by some authors either as a metal or a non-metal. Tellurium has a polyatomic (CN 2) hexagonal crystalline structure. It is a semiconductor with a band gap of 0.32 to 0.38 eV. Tellurium forms covalent bonds with most other elements, noting it has an extensive organometallic chemistry and that many tellurides can be regarded as metallic alloys. The common oxide of tellurium (TeO2) is amphoteric. Tellurium forms a series of anionic tellurites and tellurates such as Na2TeO3, Na6TeO6, and Rb6Te2O9 (the last containing tetrahedral and trigonal bipyramidal anions), as well as Zintl phases such as NaTe3.
