Tellurium
Tellurium makes chemical compounds in several oxidation states: -2, +2, +4, and +6. -2 compounds are normally found in tellurides. They are strong reducing agents. 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 tellurites and tellurous acid. They are weak oxidizing agents, that can be reduced to tellurium. Tellurites are made by reacting tellurium dioxide with a metal oxide. +6 compounds are found in tellurates and telluric acid. They are powerful oxidizing agents. Tellurates are made by reacting telluric acid with metal oxides.