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 electronpair
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 electronexchange 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 mathematicsshy chemists, Pauling did not present
lengthy mathematical proofs of his rules, for, as he wrote in the paper, "even the
formal justification of the electronpair 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
midFebruary 1931, Pauling mailed his work to the JACS. He titled the paper, somewhat
grandly, "The Nature of the Chemical Bond."
