He was following the lead of one of his scientific heroes: the legendary, cigar-chomping head of chemistry at Berkeley, Gilbert Newton Lewis. In the early 1920s, Lewis published an idea about the bonds between atoms that he had developed with General Electric researcher Irving Langmuir. They theorized that an element’s valence arose naturally from its atomic structure. Atoms, it was known, consisted of a positively charged nucleus surrounded by negatively charged electrons. Lewis and Langmuir hypothesized that atoms were most stable when the electrons orbited the nucleus in shells containing eight at a time (except for the atom’s innermost shell, which contained two electrons).

According to the Lewis and Langmuir model, if an atom had seven electrons in an outer shell, it would tend toward collecting an eighth for maximum stability. One way to do this was to combine with another atom that had one extra electron in its outer shell. The two atoms would "share" an electron, creating a more stable product. The resulting "shared electron bond" tied the atoms together into a molecule.

Pauling was intrigued by the Lewis and Langmuir model, but he knew that it was too simple to explain a number of laboratory observations about real molecules. In addition, he learned in Europe that the sort of atomic structure Lewis and Langmuir used in their model — one in which electrons orbited the nucleus like little planets — was in the process of being discarded. The new quantum physics was bringing to light an entirely new, paradoxical and exciting view of the atom. And it was on the foundation of this new science that Pauling intended to build a new understanding of the chemical bond.