Gain coefficient, definition

As the chemist has gained his sea legs in the use of wave mechanics he has attempted to define covalent and ionic character in terms of wave functions. The new point of view is presented, for example, by Coulson, who maintains, there are two distinct definitions of a covalent bond (447, p. 145). He proceeds to describe the bond wave function, first by a molecular orbital type approximation, and then by a valence bond type approximation. In either case the approximate wave functions consist of linear combinations of atomic orbitals. Partial ionic bonding is revealed by the magnitudes of coefficients which imply asymmetry of electron distribution. 

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