Science Fair Project Encyclopedia
The chalcogens 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). Their compounds, particularly the sulfides, selenides, and tellurides are collectively known as chalcogenides.
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.
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).
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