The Group 16 Elements S, Se, Te, Po

Some properties of the elements in Group 16 are given in Table 12-1. They are commonly called the chalcogens. 

In addition to such divalent species, the elements form compounds in formal oxidation states IV and VI with four, five, or six bonds tellurium may give an 8-coordinate ion TeFg . Some examples of compounds of Group 16 elements and their stereochemistries are listed in Table 12-2. They also form cyclic and polycyclic cations (e.g., S2+, Te +) under special conditions. 

The lower electronegativities of the S—Po elements lessen the ionic character of compounds that are formally analogous to those of oxygen, alter the relative stabilities of various kinds of bonds, and drastically lessen the importance of hydrogen bonding, although weak X—H - S and S—H—X bonds do exist. 

The maximum coordination number is not limited to 4, nor is the valence limited to 2, as in the case of oxygen, since d orbitals may be utilized in bonding. Thus sulfur forms several hexacoordinate compounds (e.g., SF6), and for tellurium 6 is the characteristic coordination number. 

Sulfur has a strong tendency to catenation, which manifests itself not only in the many forms of the element that all contain S rings of various sizes, but in polysulfide ions S - which may be discrete in highly ionic salts or serve as chelating ligands towards transition metals, sulfanes (XS X) (where X 

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Oxygen (O) and sulfur (S) are among the most important elements in industry, the environment, and organisms. Selenium (Se), tellurium (Te), radioactive polonium (Po), and newly synthesized element 116 lie beneath them in Group 6A(16) [Family Portrait, p. 444]. 

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