Selenide

A selenide is a chemical compound containing a selenium anion with oxidation number of −2 (Se²⁻), much as sulfur does in a sulfide. The chemistry of the selenides and sulfides is similar. Similar to sulfide, in aqueous solution, the selenide ion, Se²⁻, is prevalent only in very basic conditions. In neutral conditions, hydrogen selenide ion, HSe⁻, is most common. In acid conditions, hydrogen selenide, H₂Se, is formed.

Some selenides are reactive to oxidation by air. Owing to the greater reducing power of selenide, metal selenides are more easily decomposed to the elements than are sulfides (tellurides are even more labile). Selenides of electropositive metals: such as aluminium selenide readily hydrolyse, even in moist air, evolving toxic hydrogen selenide gas.

Pure selenide minerals are rare, instead selenium tends to partially substitute for sulfide in many sulfide minerals. The degree of substitution is only of commercial interest for copper sulfide ores, in which case selenium is recovered as a by-product of copper refining. Some selenide minerals include ferroselite and umangite.