Linus Pauling and The Nature of the Chemical Bond: A Documentary History Narrative  
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Making A Choice
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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.

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See Also: "Recipe of Mulliken, Hund, Wigner-Witmer, Herzberg, Lennard-Jones." November 1928. 
See Also: Notes on "Assignment of Quantum Numbers for Electrons in Molecules. III. Diatomic Hydrides." By Robert Mulliken. May 1929. 

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Picture
Ava Helen and Linus Pauling. 1933.


Page 1
"sp3d5 eigenfunctions." June 6, 1931.

"Attempts to regard a molecule as consisting of specific atoms or ionic units held together by discrete numbers of bonding electrons or electron pairs are considered as more or less meaningless."

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