|The Nature of the Chemical Bond
Over the next two months he worked hard polishing and expanding his findings into what would become one of the most important
papers in the history of chemistry. In it he presented six rules for the shared electron bond. The first three, restatements
of Lewis's, Heitler's, and London's, and his own earlier work, noted that the electron-pair bond was formed through the interaction
of an unpaired electron on each of two atoms; that the spins of the electrons had to be opposed; and that once paired, the
two electrons could not take part in additional bonds. His last three rules were new. One stated that the electron-exchange
terms for the bond involved only one wave function from each atom; another, that available electrons in the lowest energy
levels would form the strongest bonds. Pauling's final rule asserted that of two orbitals in an atom, the one that could overlap
the most with an orbital from another atom would form the strongest bond and that the bond would tend to lie in the direction
of that concentrated orbital. This allowed the prediction and calculation of bond angles and molecular structures.
Appropriately for his audience of mathematics-shy chemists, Pauling did not present lengthy mathematical proofs of his rules,
for, as he wrote in the paper, "even the formal justification of the electron-pair bond in the simplest cases. . . requires
a formidable array of symbols and equations." But he outlined the way others could work through the proofs and presented a
number of examples of his reasoning at work.
From the principles of quantum mechanics he was now able to derive everything from the strengths and arrangements of bonds
to a complete theory of magnetism in molecules and complex ions. Even better, using his new system Pauling was also able to
predict new electronic structures and properties for atoms. Quantum mechanics, in other words, did not just confirm what was
already known; it pointed the way to new insights. In mid-February 1931, Pauling mailed his work to the JACS. He titled the
paper, somewhat grandly, "The Nature of the Chemical Bond."