Electronic Explanations of the Periodic System Developed by Chemists

Given the advances in explanations of the periodic system provided by physicists in the first quarter of the twentieth century, described in chapter 7, it is interesting to consider what advances, if any, chemists achieved during the same period. Unlike physicists, chemists were working largely inductively with experimental data on the elements and not via any theoretical arguments. However, in many instances, the electronic configurations proposed by chemists were superior to those postulated by such physicists as Niels Bohr and Edmund Stoner. This is not entirely surprising given the chemist’s familiarity with the properties of the elements. Inductive arguments based on the macroscopic behavior of elements were often more fruitful than the deductive arguments based on physical principles. Moreover, as described in chapter 7, even physicists’ routes to electronic configurations were not always as deductive as their authors claimed them to be. The starting point for the chemical contributions to the assignment of electronic configurations can be regarded as J.J. Thomson’s discovery of the electron in 1897, since without the existence of this particle there could be no electronic configurations. In 1902, the American chemist Gilbert Norton Lewis began speculating about the electronic structure of atoms, although he did not publish his views due to the prevailing empiricist climate in US chemistry, which was rather hostile toward theoretical approaches. Considerably later, Lewis recalled his early thoughts on the constitution of atoms: . . . In the year 1902 (while I was attempting to explain to an elementary class in chemistry some of the ideas involved in the periodic law) becoming interested in the new theory of the electron, and combining this idea with those implied in the periodic classification, I formed an idea of the inner structure of the atom which, although it contained certain crudities, I have ever since regarded as representing essentially the arrangement of electrons in the atom. . . . Some dated fragments of this work still survive, including a diagram in which Lewis depicts the electronic structures of the elements from helium up to fluorine.