GROUP 12: ZINC, CADMIUM, AND MERCURY

Group 12 substance have the electron design (n-1)d10ns2 with n=4, 5 and 6 for Zn, Cd and Hg, respectively. They are formally part of the d block but the electrons of the (n-1)d shell are too rigidly bound to be involved directly in chemical bonding, and these elements give typical post-transition metal behavior. The extra nuclear charge accumulates with filling the d orbitals leads to high ionization energies in comparison with group 2 elements and hence reduced electropositive character. This is announced with mercury, which forms few compounds that may be regarded as ionic.

The substances are found in nature as sulfides, especially ZnS (zinc blende or sphalerite) and HgS (cinnabar). Overall abundances in the crust are low. Zinc is an important element of life; Cd and Hg are not require and are very toxic.

The elements can be produce by reduction of sulfides or oxides. Cadmium and zinc are needs for corrosion-resistant coatings. The metals have boiling and melting points that are lower than for group 2 elements, especially with Hg, which is one of two elements (Br being the other) presents as a liquid at 25°C. Cd and Zn are more reactive than Hg, dissolving in non-oxidizing acids and forming oxide films in air. Mercury oxidizes at room temperature but HgO break readily on heating, a reaction historically important in the discovery of oxygen. Mercury dissolves several metallic elements to form amalgams, which may be useful reagents.