ZINC GROUP ELEMENT

Figure 1: Modern version of the periodic table of the elements. To see more information about an any of the three metals that comprise Group IIb of the periodic table of elementsnamely, zinc (Zn), cadmium (Cd), and mercury (Hg). (See Figure.) They have properties in common, but they also differ in significant respects. All three are metals with a silvery-white appearance and relatively low melting points and boiling points; mercury is the only common metal that is liquid at room temperature, and its boiling point is lower than that of any other metal. The three elements are found in different proportions in the Earth's crust: it has been estimated that zinc is present to the extent of 80 parts per million (compared with 70 for copper and 16 for lead). The estimate for cadmium is only 0.15; commercially, it is always found associated with zinc or zinclead ores and is produced only as a by-product of zinc and lead smelting. The proportion of mercury in the Earth's crust is estimated at 0.08 parts per million. All important mercury deposits consist of mercuric sulfide, known as the mineral cinnabar. Additional reading A general view of the principles underlying the extraction of zinc, cadmium, and mercury is given in Donald M. Liddell (ed.), Handbook of Nonferrous Metallurgy, 2nd ed., 2 vol. (1945). The toxicity of the three metals is dealt with in Ethel Browning, Toxicity of Industrial Metals, 2nd ed. (1969). A useful summary of the behaviour of mercury is found in Eric N. Simons, Guide to Uncommon Metals (1967). More information on these three metals is provided in C.A. McAuliffe (ed.), The Chemistry of Mercury (1977); Leonard J. Goldwater, Mercury: A History of Quicksilver (1972); D.M. Chizhikov, Cadmium (1966; originally published in Russian, 1962); Marie Farnsworth, Cadmium Chemicals (1980); S.W.K. Morgan, Zinc and Its Alloys and Compounds (1985); Helmut Sigel and Astrid Sigel, Zinc and Its Role in Biology and Nutrition (1983); and Marie Farnsworth, Charles H. Kline, and J.G. Noltes, Zinc Chemicals (1973). Stephen William Kenneth Morgan The Editors of the Encyclopdia Britannica