In his 1928 note, Pauling proposed an explanation based on Heitler and London’s electron exchange energy. Each time a new bond was created, new exchange energy was involved. The electron exchange energy resulting from forming four tetrahedral bonds, he wrote, was sufficient to break carbon’s four binding electrons out of the physicists’ subshells and allow them to assume new, equivalent forms.

This was an exciting idea, but one that would have to be backed up with considerable mathematics. Pauling didn’t present any in his note, however, writing that "the detailed account of the material mentioned in this note will be submitted for publication in the Journal of the American Chemical Society."

Nearly three years would pass before Pauling’s "detailed account" appeared. In 1928 he had worked through enough convoluted calculations to convince himself, at least preliminarily, that his idea was right, but "it was so complicated that I thought people won’t believe it," he said. "And perhaps I don’t believe it, either. . . . Anybody could see that the quantum mechanics must lead to the tetrahedral carbon atom, because we have it. But the equations were so complicated that I never could be sure that I could present the arguments in such a way that they would be convincing to anybody."