The Semiempiricist

After finishing his first paper on the nature of the chemical bond, in 1931, Linus Pauling stopped basing his ideas on mathematical proofs. Chemists, he understood, were not trained to appreciate the difficult mathematics of quantum physics. To communicate with them, he developed his own theoretical style, made up in equal parts of a broad application of Erwin Schrodinger's wave mechanics, structural data from X-ray crystallography, other laboratory results from across the field of chemistry, and Pauling's own insights.

Observers termed Pauling's approach semiempirical, meaning that it was neither pure theory nor the simple marshaling of laboratory results. Whatever it was, it was tremendously successful. Using it, Pauling was able to answer long-standing questions about the nature of molecules, show that chemical bonds existed in a range of forms never imagined before, and rebuild chemistry on a new foundation provided by quantum mechanics.

Of all the world's scientists, only Pauling in the 1930s could fit together all these pieces of the puzzle. When he came up with a new idea about the chemical bond, he could immediately test it by comparing his thought structures with real ones discovered in his crystallography laboratory. And when a crystallographer proposed a new structure, Pauling could see if it was reasonable according to the rules of quantum mechanics. He constantly checked and cross-checked all of his new theoretical ideas against the known properties of molecules, their melting and boiling points, reactivity, and thermodynamic behavior.

Guiding Pauling's work was his fervent belief that molecular function was explained by molecular structure. Molecules had their own architecture, measured in billionths of inches, and Pauling's great drive was to be the first to describe as many of these structures as possible— thereby gaining new understanding about how they behaved.

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