The Pair Bond Theory of Valency

Abstract

THE method of molecular orbitals (Hund, Mulliken, Lennard-Jones), which is especially designed for the description of a completed molecule can be worked out in high approximations only in the simplest cases. In more complicated ones, it is therefore not able to describe the process of dissociation, which is clearly the essential requirement of a theory of valency. Accordingly it is necessary to resort to the correlation table which, however, gives only qualitative results, and no information regarding the quantitative loss or gain of energy. An additional assumption is therefore necessary, and this is found in the hypothesis that bonding power is always ascribed to the lowest one of a group of terms, resulting from the same atomic term by splitting due to the removal of a degeneracy. The wave-function of this term in the case of one electron linking the two cores A and B isin the case of two electrons. The wave-function (1) shows that a linkage can be brought about by a single electron only if the atomic fields in question are either equal (a = b) or almost equal (a b), and this is why the method of molecular orbitals has recently been interpreted as leading to a single-electron bond theory. When the degeneracy of the fields gradually disappears, function (1) becomes, however, simply A or B, whichever is lower, showing that the bonding power ceases when the difference between the eigen-values of A and B is no longer negligible.