What is Tellurium?
[[File:Tellurium crystal.jpg|thumb|A very [[purity|pure]] tellurium [[crystal]]]] '''Tellurium''' is a [[chemical element]]. It has the chemical symbol '''Te''' and the [[atomic number]] 52. It has 52 [[proton]]s and 52 [[electron]]s. Its [[mass number]] is 127.6. It has 8 natural [[isotope]]s. 4 are stable and 4 are [[radioactive]]. One of the radioactive ones lasts longer than any other isotope. It has a [[Half-life (element)|half life]] of 2.2 x 10<sup>24</sup> years (2.2 septillion years). ==Properties== ===Physical properties=== [[File:Tellurium'.jpg|thumb|Tellurium in a tube]] It is a [[wikt:brittle|brittle]] silver-white [[semimetal]]. When it is pure it has a metallic shine. It is ground easily. It can be made in an amorphous form. It is a [[semiconductor]]. It changes conductivity a little when light shines on it, similar to [[selenium]]. It is corrosive to many metals when molten. ===Chemical properties=== Tellurium is an unreactive element. It can react with reactive metals to make tellurides. It can burn in air to make [[tellurium dioxide]]. It can be [[oxidation|oxidized]] even more to [[tellurium trioxide]]. It does not [[corrosion|corrode]]. The chemistry of tellurium is similar to some chemistry of [[selenium]] and [[sulfur]], although its compounds are more reactive and the element is less reactive. It does not dissolve in most acids, although it dissolves in concentrated [[sulfuric acid]] to make a special red tellurium cation. ===Chemical compounds=== {{see also|Category:Tellurium compounds}} Tellurium makes [[chemical compound]]s in several [[oxidation state]]s: -2, +2, +4, and +6. -2 compounds are normally found in [[telluride]]s. They are strong [[reducing agent]]s. Tellurides are normally the main ore of tellurium. Most natural tellurides are not pure, so they are much less reactive. +2 compounds are found in some tellurium halides, like [[tellurium(II) chloride]] and [[tellurium(II) bromide]]. They are the rarest oxidation state. +4 compounds are found in [[tellurite]]s and [[tellurous