A selenide is a chemical compound in which selenium serves as an anion with oxidation number of −2 (Se2−), much as sulfur does in a sulfide. The chemistry of the selenides and sulfides are similar.
Similar to sulfide, for an aqueous solution, 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, although the degree of substitution is only of commercial interest for copper sulfide ores. Selenium is thus recovered as a by-product of copper mining. Some selenide minerals include ferroselite and umangite.[1]