Chalcogen

Overview
The chalcogens (with the "ch" pronounced like a k) are the name for the periodic table group 16 (old-style: VIB or VIA) in the periodic table. It is sometimes known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), the radioactive polonium (Po), and the synthetic ununhexium (Uuh). The compounds of the heavier chalcogens (particularly the sulfides, selenides, and tellurides) are collectively known as chalcogenides. Unless grouped with a heavier chalcogen, oxides are not considered chalcogenides.

The name is generally considered to mean "ore former" from the Greek chalcos "ore" and -gen "formation". 

Oxygen and sulfur are nonmetals, and polonium, 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.

Chalcogens are quite common as minerals. For example, pyrite (FeS2) is an iron ore and AuTe2 gave its name to the gold rush town of Telluride, Colorado in the United States.

The formal oxidation number of the chalcogen is generally -2 in a chalcogenide but other values, such as -1 in pyrite, can be attained.

The highest formal oxidation number +6 is found in sulfates, selenates and tellurates, such as in sodium selenate (Na2SeO4). Modern chemical understanding based on quantum theory somewhat outdates the use of formal oxidation numbers in favour of a many-electron wavefunction approach allowing detailed computer simulation, though the concept, while flawed, is still useful in thought experiments.