SULFUR, SELENIUM AND TELLURIUM
The elements known commonly as the chalcogens are in the same group (16) as oxygen. They form some compounds same to those of oxygen, but show many differences characteristic of other nonmetal groups. Sulfur is widespread in the Earth's crust, finding as metal sulfides, sulfates, and native or elemental sulfur build by bacterial oxidation of sulfides. Many less electropositive metals known as chalcophiles are collect commonly as sulfide minerals, some important examples are sphalerite (zinc blende, ZnS), pyrites (FeS2), molybdenite (MoS2), galena (PbS) and cinnabar (HgS). Volatile sulfur compounds such as organic compounds and H2S are also collect in petroleum and natural gas. The element is used in bigger amounts for the manufacture of sulfuric acid (see below).
Tellurium and selenium are much rarer, found as minor components of sulfide minerals.
Sulfur has various allotropic forms, the most stable of which are molecular solids containing S8 rings. The elemental forms of Te and Se have spiral chains and are semiconductors. In all of those solids each atom forms two single bonds to neighbors. Sulfur collides directly with halogens (except I) and oxygen, and with many less electronegative elements to form sulfides. The other elements show same properties although reactivity declines down the group.