The Group 12 consists of three metals: zinc (Zn), cadmium (Cd), and mercury (Hg). Their oxidation states usually are not higher than +2 (Table 17.1).

They all are relatively mobile in the Earth’s surface and their cycling may be highly modi ed by the accumulation by plants and organic debris. These metals have comparatively high electronegativity values and easily form bonds with other elements, especially with S anions and with several organic compounds. Thus, they all are of great importance in the biochemistry. Although sul des of Zn, Cd, and Hg are insoluble in water, compounds of Zn and Cd immediately hydrolyze, but the corresponding compounds of Hg are rather resistant to hydrolysis. The toxicity of Cd and Hg is well known, whereas Zn has enormous biological importance.