Chalcogen

The chalcogens are the name for the chemical series Group 16 (old-style: VIB or VIA) in the Periodic Table.
It consists of the elements Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), and the radioactive Polonium (Po).

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