Chalcogen 

Their compounds, particularly the sulfides, selenides and tellurides are collectively known as chalcogenides. A term like 'chalcides' might have been a more logical derivative from chalcogen, like halide is from halogen, but the scientific language is -like any language- not always logical.

The name is generally considered to mean "ore former" from the Old Greek chalcos "ore" and -gen "formation". [1] (http://jchemed.chem.wisc.edu/Journal/Issues/1997/Sep/abs1063.html)

Oxygen and sulfur are nonmetals, polonium is a true metal[?], and selenium and tellurium are metalloid semiconductors (i.e., their electrical properties are between those of a metal and an insulator). Nevertheless, tellurium, as well as selenium, is often referred to as a metal when in elemental form.

Chalcogenides are quite common as minerals. E.g. FeS₂ pyrite is an iron ore and AuTe₂ gave its name to the gold rush town of Telluride in Colorado US.

The oxidation number of the chalcogen is generally -2 in a chalcogenide but other values (e.g. -1 in pyrite) can be attained.

The highest oxidation number +6 is found in sulfates, selenates and tellurates, e.g. in Na₂SeO₄ sodium selenate

See also: Periodic table of elements

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