Along with the doctrine of atomism, the electron theory of valance ranks as one of the most fundamental developments in the history of modern chemistry. Yet, because the problems this theory solved were difficult ones, the modern understanding of electron bonding came only slowly and only after the minor contributions of many scientists and the major contributions of a few. Following the discovery of the electron by J. J. Thomson at Cambridge in 1897, scientists quickly concluded that the bonds holding atoms in a molecule were electrostatic or polar and resulted from complete electron transfer. Soon, though, other chemists pointed out that the behavior of many organic molecules was inconsistent with the polar theory. Despite the work of many scientists, it was not until 1916 that one---G. N. Lewis---succeeded in putting forward the currently accepted electronic mechanism for the non polar bond---the shared electron pair.

In this lucidly written and carefully documented study, the author traces the gradual transition from a purely polar theory to one requiring two kinds of bonds, polar and nonpolar, and demonstrates that Lewis, with his far-reaching idea of the shared electron pair bond, was the central figure in this scientific drama.

The focus on Lewis and other major researchers and the detailed attention to more minor actors illustrate both how individual contributions to the solution of perplexing problems fit within general trends and how one individual mind can rise above an era's state of knowledge to advance science.

The coherent story told here helps meet a great need for the historical study of recent periods in the development of the sciences and should appeal not only to chemists but to all interested in the history of science and the history of thought.