For a few years it looked as if chemists would be forced to choose either Pauling's view or Mulliken's. But at root the two
approaches were not as different as they seemed. Both were based on Schrödinger's wave equation, and Slater and others found
in the mid-1930's that if the mathematics was carried through far enough, the two approaches ended up providing the same results.
It was rather like the choice physicists had to make between Heisenberg's matrix approach to quantum mechanics and Schrödinger's
wave equation: Although seemingly very different, both were paths to the same destination. The choice of the paths depended
on which was easier to use and which worked better in a given situation.
Pauling, of course, thought his was the better approach to understanding the chemical bond. He understood that the molecular-orbital
approach was useful - he had employed it in some cases while searching for a breakthrough on the chemical bond - but he largely
dropped it when he found how to make his own variations on the Heitler-London theme work in 1931. Once Slater showed the essential
equivalence of his and Mulliken's methods, Pauling saw no need to refer to the molecular-orbital approach. His ideas worked
out of what chemists already believed about the chemical bond; Mulliken's were by comparison anti-intuitive and, Pauling thought,
confusing to students.
And Pauling's notion of the chemical bond took off, while Mulliken's languished in relative obscurity. There were several
reasons, prominent among them the fact that Pauling was an eloquent teacher and a persuasive writer who knew how to communicate
in language chemists could understand. When Pauling spoke, the valence-bond approach seemed like revealed wisdom. When Mulliken
talked, people went to sleep. He was a terrible teacher, ill at ease in front of crowds, his voice almost inaudible. He refused
to pander to his chemistry students, and his lectures were notoriously digressive, heavy with mathematics, and hard to follow.
He was not much better in print. As the years went by, Mulliken and a small band of followers would continue to improve their
molecular-orbital approach, refining the equations and using it successfully to attack a number of problems. Twenty years
later, a new generation of chemists would come to prefer it over Pauling's approach. But in the 1930's, Mulliken's ideas would
be lost in a blizzard of results blowing out of Pasadena.