The Structure of Discovery: Evolution of Structural Accounts of Chemical Bonding

Abstract

In their important 1927 paper, Werner Heitler and Franz London provided the first qualitative explanation of the chemical bond on the basis of quantum mechanics. Their application of Schrödinger’s equation to the simplest molecule appeared to elucidate the physical basis of the covalent bond, and thereby initiated ‘quantum chemistry’. Although the numerical results (for bond length and bonding energy) were only roughly in agreement with the experimentally determined values, the theory was regarded as a great success and, according to Slater (1975, p. 93), “produced a sensation among physicists.” The recognition given to the work of Heitler and London by both chemists and physicists, the extent to which subsequent work in the quantum structure of molecules (particularly valence bond theory) is based upon the methods introduced (or at least made use of) in the Heitler-London theory, and the continued use even of the terminology Heitler and London employed in their interpretation of approximate solutions for the bound state of the electrons and the binding energy (‘overlap integral’, ‘exchange energy’, for example) all point to the significance of the Heitler-London theory of the hydrogen bond as a theoretical discovery. In this paper I am going to take this theory, and the path to it, as an example of a discovery of a theoretical description or account which at the same time bridges two fields of science (or points toward a ‘unification’ of those fields or ‘incorporates one field into’ another) and is the basis of a great deal of further scientific work on similar problems (the source of a ‘research program’ or minor ‘scientific paradigm’).