ZINC-GROUP ELEMENT

any of three metals that comprise Group IIb of the periodic table of elementsnamely, zinc (Zn), cadmium (Cd), and mercury (Hg) (qq.v.). All three zinc-group elements are found in the Earth's crust, but they are never in the free state (uncombined). They are silvery white in colour and have comparatively low melting points and boiling points. The boiling point of mercurythe only common metal that is liquid at room temperatureis lower than that of any other metal. The zinc elements exhibit similar chemical behaviour because of certain affinities in their atomic structure. The atoms of these elements are able to lose two electrons in their outermost shells to form divalent positive ions, thereby exposing the next innermost shell with a stable configuration of 18 electrons in each case. Ordinary chemical reactions cannot supply enough energy to remove more than two electrons and thus increase the valency above 2. The zinc-group elements tend to utilize their two outer electrons for covalent bonding. This tendency is most distinct in the case of mercury, less so in that of zinc, and least with cadmium.