A Classic of Twentieth-Century Science: The Nature of the Chemical Bond

Portrait of Linus Pauling, 1930s

Portrait of Linus Pauling. 1930s.

“I have just returned from a short vacation for which the only books I took were a half-dozen detective stories and your ‘Chemical Bond’. I found yours the most exciting of the lot.”
– G.N. Lewis. Letter to Linus Pauling. August 25, 1939.

In the fall of 1930, Pauling began work on a determination of the structure of the carbon tetrahedron, implementing the simplified version of the Schrödinger wave equation as modified by John C. Slater. Pauling’s goal was to define the atomic architecture of the carbon tetrahedron, as it was understood by chemists, in terms of quantum mechanics. Success in this venture carried with it the potential to unify chemists and physicists in their understanding of molecular bonding.

Pauling worked through the fall without any major breakthroughs until finally, in December of 1930, he made the decision to remove the radial function from his equation in an attempt to simplify the mathematics of the project. Having done so, Pauling found that the resulting wave functions, (which might be thought of as mathematical models of atomic structures derived from x-ray studies of substances) when mathematically combined, resulted in four hybrid orbitals oriented at the angles of a tetrahedron. Moreover, the mathematics demonstrated that bonds strengthened as the overlap between orbitals increased.

Pauling was elated to find that all variables could be accounted for using his new mathematical method. It was immediately clear to the 29-year-old scientist that this was a major discovery. In his own words,

“I was so excited and happy, I think I stayed up all night, making, writing out, solving the equations, which were so simple that I could solve them in a few minutes. Solve one equation, get the answer, then solve another equation about the structure of octahedral complexes such as the ferrocyanide ion in potassium ferrocyanide, or square planar complexes such as in tetrachloroplatinate ion, and various other problems. I just kept getting more and more euphorious as time went by.”

In February of 1931, Pauling mailed his paper to the Journal of the American Chemical Society. Boldly titled “The Nature of the Chemical Bond: Application of results obtained from the quantum mechanics and from a theory of paramagnetic susceptibility to the structure of molecules,” Pauling’s publication was promptly recognized to be an instant classic of twentieth-century science.

The paper defined six rules for the shared electron bond and presented his findings in uncomplicated terms, allowing his colleagues to examine his research without becoming lost in the mathematics. Pauling’s write-up was distributed in J.A.C.S. only six weeks after the manuscript arrived in the journal’s offices. The incredible speed of this turn-around from manuscript to print was abetted by the fact that the paper had not been refereed, as J.A.C.S. editor Arthur Lamb could think of no individual properly-qualified to review the revolutionary content of Pauling’s work.

Pauling’s unique combination of chemistry and quantum mechanics reinforced the accumulated knowledge of both fields and, in an invaluable breakthrough, pushed researchers toward an understanding of completely new atomic structures and properties. The importance of Pauling’s discovery only grew with time — that, and the publication by Pauling of six more papers on the topic.

In 1939, Pauling collected his research into an extremely popular textbook titled The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry. The text was a huge success on many levels: not only did it describe research of fundamental importance to the study of chemistry, but it did so in a lucid style that was understandable to a wide range of users. As Max Perutz would later note, The Nature of the Chemical Bond proved that “chemistry could be understood rather than being memorized.” A contemporary of Pauling’s, Dr. Charles P. Smyth, would echo this perspective in a 1939 letter, writing:

“I have been very much interested by your new book and have assigned several of the chapters for reading in connection with a graduate course. As evidence of my interest in it, I can cite the fact that it is the first scientific book which I can remember reading during the course of a fishing trip, although I have carried many with me in the past.”

It is likewise worth noting that various editions of The Nature of the Chemical Bond can still be found for sale online, nearly eighty years after its first printing and fifteen years after it’s author’s death. While some of the research presented in its pages is now outdated, the clarity and impact of its writing insures its status as one of the great scientific publications of all time.

Read the original manuscript for the first “Nature of the Chemical Bond” paper and learn much more about this important story on the website “Linus Pauling and the Nature of the Chemical Bond: A Documentary History.”

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