In the late 1920s, Pauling was one of just three young Americans — the others were John Slater at MIT and the University of Chicago’s Robert Mulliken — who could combine a deep understanding of the new physics with a strong interest in solving chemical questions. Of the
three, Pauling had the strongest training in basic chemistry.
More direct competition for Pauling’s goal of explaining the chemical bond in quantum mechanical terms came from two young
researchers, Walter Heitler and Fritz London. Heitler and London, working closely with Erwin Schrödinger, had been the first to apply Schrödinger’s wave equations to
the question of the simplest chemical bond, that between two hydrogen atoms.
They took advantage of a new idea of Heisenberg’s, something he called exchange energy. The theory proposed that as two atoms
approached each other the chances would increase that a negatively charged electron from one would find itself attracted to
the positively charged nucleus of the other, and the same thing would happen from the other side. At a certain point, the
two electrons would begin jumping back and forth between the two nuclei, creating an electron exchange at a rate of billions
of times per second. In a sense, the two electrons would not be able to tell which nucleus they belonged to.
Combining that concept with Schrödinger’s wave equation, Heitler and London calculated that the attraction made possible by
the electron exchange would be balanced at some point by the repulsion of the two positively charged nuclei, creating a chemical
bond with a definite length and strength. They demonstrated the idea by applying the mathematics to the binding of two hydrogen
It was a great triumph. Pauling became convinced that their approach was correct when he was in Europe. But this was just
a first step in a potentially huge field, worked out only for the simplest molecule possible. There were many other problems
to solve. And Pauling would be the one to solve them.
"I thought there was a possibility of doing something better, but I didn’t know what it was that was needed to be done," Pauling
remembered. "I had the feeling that if I worked in this field I probably would find something, make some discovery, and the
probability was high enough to justify my working in the field."