Chalcogen

Chalcogen is the general name given to the elements of group 16 of the periodic table, the column headed by oxygen. This group includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). The very heavy synthetic element livermorium (Lv) also occupies this group, but its chemical properties remain poorly understood.

The defining chemical feature of the group is that its atoms have six electrons in the outermost (valence) shell. Consequently, they commonly gain two additional electrons or share electrons to achieve stability, forming compounds with a charge state of −2, and can also display higher oxidation states such as +4 and +6 when bonded to highly electronegative elements.

Name and origin

The word "chalcogen" derives from Greek, meaning something related to ore production or the birth of copper ore. The term reflects the fact that many naturally occurring important ores consist of sulfides (sulfur compounds) and oxides (oxygen compounds). Consequently, compounds of this group are called chalcogenides.

Variation of properties within the group

Moving down the group from top to bottom, the character transitions from clearly nonmetallic to metallic. Oxygen and sulfur are pronounced nonmetals; selenium is a semiconductor with intermediate properties; tellurium is classified as a metalloid; polonium displays metallic character and is radioactive. At the same time, atomic radius increases, while electronegativity and the tendency to attract electrons decrease.

Uses and natural occurrence

Oxygen is fundamental to respiration and combustion, and is a component of water and rocks. Sulfur is used to make sulfuric acid, an enormous industrial chemical, and for vulcanization of rubber. Selenium and tellurium are used in electronic devices, semiconductors, and photocells. Polonium, owing to its radioactivity, has limited application and must be handled with care.