The Physico-chemical Nature of the Chemical Bond: Valence Bonding and the Path of Physico-chemical Emergence

Through the development of physical chemistry and chemical physics over the late-nineteenth and early-twentieth centuries, the relationship between physics and chemistry changed to create a broad interdisciplinary framework in which chemists and physicists could make contributions to problems of common value. It is here argued that evolving disciplinary factors such as physical and chemical responses to the atomic hypothesis, the nature of disciplinary formation in Germany and the United States, the reception of quantum mechanics within physics and chemistry, and the application of quantum mechanics to the problem of chemical bonding by physicists and chemists, formed the chemical bond into a physico-chemical theory. In the late nineteenth-century context of early physical chemistry, the chemical bond was known as a physical link between atoms, which could not be studied by chemical means because of the lack of an adequate atomistic framework. Both chemists and physicists broadly accepted the atomistic hypothesis following the discovery of the electron at the turn of the twentieth century, which afforded theoretical study of chemical bonding. Between 1916 and 1919, Gilbert N. Lewis and Irving Langmuir proposed the valence bond to be a pair of electrons shared between two atoms, within the context of a cubic model of the atom. However, the lack of a physical mechanism for the shared electron pair prevented the formation of a fully physico-chemical view of bonding. In 1927, physicists Walter Heitler and Fritz London showed the stability of the valence bond was caused by the wave mechanical phenomenon of resonance. Chemist Linus Pauling extended their treatment of the valence bond to a theory of structural chemistry in The Nature of the Chemical Bond. His synthesis of the physical and chemical views, his value as a physico-chemical researcher during the 1930s, and the research of his contemporaries John Slater and Robert Mulliken show that a true physico-chemical blend was only realized within the amorphous discipline of chemical physics. Finally, it is seen that this interdisciplinarity of chemical bonding and its supporting framework force a reevaluation of the reductionist criteria, and a re-definition of the chemical bond as a physico-chemical work.Ph