BONDING IN CARBIDES, SILICIDES, AND BORIDES

Abstract

The hypothesis that many of the properties of the transition metal, their alloys, and their compounds can be understood in terms of a relationship between the co-ordination of the metal atoms and the number of bonding electrons per atom, is applied to the carbides, silicides, and borides of the transition metals of Groups IVA, VA, and VIA. The crystal structure and stability of the carbides can be satisfactorily explained on the basis of electron concentration, but a complete understanding of the bonding in the silicides and borides is more difficult. In the silicides the metal–silicon bonding, which is metallic in character, becomes of increasing importance as the silicon content is increased, and in the disilicides no direct metal–metal bonding remains. The ability of boron to form strong boron–boron bonds is important in the borides, and the metal–metal co-ordination would appear to be of only secondary importance. The practical significance of the principles put forward is discussed.