Abstract
An historical overview is given of the relevant steps that allowed the genesis of the quantum theory of the chemical bond, starting from the appearance of the new quantum mechanics and following later developments till approximately 1931. General ideas and some important details are discussed concerning molecular spectroscopy, as well as quantum computations for simple molecular systems performed within perturbative and variational approaches, for which the Born-Oppenheimer method provided a quantitative theory accounting for rotational, vibrational and electronic states. The novel concepts introduced by the Heitler-London theory, complemented by those underlying the method of the molecular orbitals, are critically analyzed along with some of their relevant applications. Further improvements in the understanding of the nature of the chemical bond are also considered, including the ideas of one-electron and three-electron bonds introduced by Pauling, as well as the generalizations of the Heitler-London theory firstly performed by Majorana, which allowed the presence of ionic structures into homopolar compounds and provided the theoretical proof of the stability of the helium molecular ion. The study of intermolecular interactions, as developed by London, is finally examined.
Highlights
IntroductionThe history of atomic physics is inextricably related to that of the quantum theory, as well known, since the development of the last one was required just by evidences claiming for an appropriate physical description of
The history of atomic physics is inextricably related to that of the quantum theory, as well known, since the development of the last one was required just by evidences claiming for an appropriate physical description ofHow to cite this paper: Esposito, S., & Naddeo, A. (2014)
Mulliken looked at a molecule as at a collection of nuclei fixed in given spatial locations and surrounded by an electron cloud (Mulliken, 1929; Mulliken, 1932a), and it was soon easy to take the step and embed each electron into a “molecular orbital” which spreads over the whole molecule: As the atoms approach each other, they lose their identity and share electrons, giving rise to the chemical bond
Summary
The history of atomic physics is inextricably related to that of the quantum theory, as well known, since the development of the last one was required just by evidences claiming for an appropriate physical description of. If polar molecules were described in terms of electrostatic interaction among the constituent atomic systems already in the framework of the old quantum theory, novel physical concepts were required even just for an approximate understanding of the chemical bond in homopolar compounds. Such concepts revealed to be genuinely quantum mechanical in nature, their emergence and physical interpretation was not at all trivial, as testified by the appearance (in the years mentioned) of a number of papers discussing different methods and viewpoints. The large amount of contributions here analyzed will be summarized in our concluding section
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