Pauling electrostatic valence principle

In 1929 Pauling proposed as the second of his Principles Determining the Structures of Complex Ionic Crystals [1], that a cation-anion bond could be characterized by the oxidation state (atomic valence) of its cation divided by its coordination number. He showed that the total amount of this quantity, usually now called the Pauling Bond Strength, received by the anion was approximately equal to the anion oxidation state. He called this the Electrostatic Valence Principle, but it is now commonly referred to as Pauling s Second Rule. 

Pauling s Electrostatic Valence Principle, or the Valence Sum Rule, as it is called in the modified form used here (see Section 10.2.3), provides a useful check on the correctness of a structure and can draw attention to problems in its chemical description. Many workers now use the Valence Sum Rule routinely as a check on the correctness of a structure determination. 

This determination of the coordination number of the ion is predicated on the electrical neutrality principle given earlier (see page 19). This principle is also called the electrostatic valence principle and is part of Pauling s second rule In a stable ionic structure the valence of each anion, with changed sign, is exactly or nearly equal to the sum of the strengths of the electrostatic bonds to it from the adjacent cations. (Pauling, 1960)... 

Although equation 11.146 agrees with the principle of electrostatic valence of Pauling (1929), normalization to the cation-to-oxygen distance R t-o lo account for bond variation... 

Pauling (1929) introduced the concept of mean strength of the bond (Si) as a ratio of the valence with coordination number. He also formulated the principle of electrostatic valence, which establishes that the sum of the mean bond strengths for a given coordination polyhedron (P) coincides with the valence state—i.e.. 

The Rule 2 of Pauling (also called the principle of electrostatic valence) refers to the local electro-neutrality and assets that in the stable ionic structures, the charge of an anion surrounded by n cations M is balanced by the sum of strengths of electrostatic bonds (abbreviated SEB = m/n) with which polyhedrally coordinates ... 

The concept of bond valence, which, as will be shown below, is the same as the bond flux derived in Chapter 2, grew out of attempts to refine Pauling s principles determining the structures of complex ionic crystals (Section 1.7). In this empirical evolution of Pauling s model, both the electrostatic and short-range components were developed simultaneously. Only later did it become apparent that it was also possible to derive the properties of the electrostatic component independently using the ionic theory. 

Soon after the development of the quantum mechanical model of the atom, physicists such as John H. van Vleck (1928) began to investigate a wave-mechanical concept of the chemical bond. The electronic theories of valency, polarity, quantum numbers, and electron distributions in atoms were described, and the valence bond approximation, which depicts covalent bonding in molecules, was built upon these principles. In 1939, Linus Pauling s Nature of the Chemical Bond offered valence bond theory (VBT) as a plausible explanation for bonding in transition metal complexes. His application of VBT to transition metal complexes was supported by Bjerrum s work on stability that suggested electrostatics alone could not account for all bonding characteristics. 

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