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.

[Easton: Mack Printing Co., 1931].

First edition, extremely rare offprint, signed by Pauling, of this landmark paper, the birth of the ‘valence bond theory’ of molecular structure and the beginning of the application of quantum mechanics to chemistry. This is “arguably Pauling’s most important contribution to science [and] it was the contribution of which Pauling himself was most proud” (Goertzel & Goertzel, Linus Pauling (1995), pp. 70-71). As students in the mid-1920s, Pauling and his colleagues worked under the prevailing theory that atoms formed molecules through rudimentary ‘hook-and-eye’ bonds conceptually similar to the types of devices used by recreational fishermen to connect their boats to the back of towing vehicles. Pauling shattered these now-archaic assumptions by applying the new quantum physics to the understanding of molecular architecture. Introducing concepts such as valency and the hybrid orbital, Pauling posited a revolutionary set of theories in which chemical bonds were created through the exchange of energy between atoms. Almost instantly the hook and eye approach was cast into oblivion – Pauling had drafted the new blueprint for modern structural chemistry. “New Scientist magazine once characterized Pauling as one of ‘the 20 greatest scientists of all time, on a par with Newton, Darwin, and Einstein.’ Pauling has also been called one of the two greatest scientists of the 20th century (the other being Einstein) and the greatest chemist since Antoine-Laurent Lavoisier, the 18th-century founder of modern chemistry” (American Chemical Society). Pauling is the only person in history to win two unshared Nobel Prizes – the 1954 chemistry prize “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances,” and the Nobel Peace Prize in 1962. ABPC/RBH lists one other copy, also inscribed (Sotheby’s, 15 June, 2006, lot 116, $6600). OCLC lists only one copy in North America, in the Ava Helen and Linus Pauling Archives at Oregon State University (scarc.library.oregonstate.edu/coll/pauling/bond/papers/1931p.3-28.html).

Provenance: Signed ‘Linus Pauling’ on title page.

In the fall of 1927, a newly hired professor – tall and energetic, with a beautiful young wife and an abundance of self confidence – arrived at the California Institute of Technology near Los Angeles. His name was Linus Pauling. He came fresh from Europe, where he had spent more than a year on a Guggenheim Fellowship participating in a scientific revolution. He did not know it, but he was about to start another at Caltech. During the next twelve years he would reshape the study of chemistry, lay the groundwork for molecular biology, write one of the most important books in scientific history and define the nature of the chemical bond. In 1954 he would win a Nobel Prize for his work …

Although trained as a chemist, he had spent his time in Europe studying theoretical physics — a passion that ran so deep he had seriously considered switching from chemistry to physics. The science he learned in Münich, Copenhagen and Zürich was a new approach to the field called quantum physics. Pauling learned about it directly from its discoverers Niels Bohr, Erwin Schrödinger, Werner Heisenberg and Wolfgang Pauli, and from its greatest teacher, Arnold Sommerfeld. Schrödinger’s approach, based on the physics of waves, especially interested Pauling because he saw that it might throw new light on questions he had pondered since he was an undergraduate: What forces held atoms together to form molecules? How did those forces give the molecules particular shapes and qualities? …

Linus Pauling intended to solve these mysteries by applying the new physics he had learned in Europe. He was following the lead of one of his scientific heroes: the legendary, cigar-chomping head of chemistry at Berkeley, Gilbert Newton Lewis. In the early 1920s, Lewis published an idea about the bonds between atoms that he had developed with General Electric researcher Irving Langmuir. They theorized that an element’s valence arose naturally from its atomic structure. Atoms, it was known, consisted of a positively charged nucleus surrounded by negatively charged electrons. Lewis and Langmuir hypothesized that atoms were most stable when the electrons orbited the nucleus in shells containing eight at a time (except for the atom’s innermost shell, which contained two electrons). According to the Lewis and Langmuir model, if an atom had seven electrons in an outer shell, it would tend toward collecting an eighth for maximum stability. One way to do this was to combine with another atom that had one extra electron in its outer shell. The two atoms would ‘share’ an electron, creating a more stable product. The resulting ‘shared electron bond’ tied the atoms together into a molecule …

“Pauling was intrigued by the Lewis and Langmuir model, but he knew that it was too simple to explain a number of laboratory observations about real molecules. In addition, he learned in Europe that the sort of atomic structure Lewis and Langmuir used in their model – one in which electrons orbited the nucleus like little planets – was in the process of being discarded. The new quantum physics was bringing to light an entirely new, paradoxical and exciting view of the atom. And it was on the foundation of this new science that Pauling intended to build a new understanding of the chemical bond …

“When Pauling arrived in Münich on his Guggenheim Fellowship in 1925, Sommerfeld’s institute was abuzz with news of a radically new approach toward understanding the atom that had been proposed by one of Sommerfeld’s former students, a young physicist named Werner Heisenberg … But then, just as the Paulings were settling into a tiny Münich apartment, a seemingly new, very different approach was presented by one of Heisenberg’s critics, the Austrian physicist Erwin Schrödinger. The two competing theories were the subject of heated debate during the entire time Pauling was in Europe. But he quickly decided which one appealed to him most.

“Heisenberg’s purely mathematical approach to the structure of the atom – based on a difficult set of matrix calculations – yielded results that matched the bewildering array of new observations physicists were making about the properties of simple atoms. But for a chemist like Pauling, trained to view atoms and molecules as real things with particular sizes and shapes, pure mathematics was unsatisfactory. He preferred Schrödinger’s theory. The old picture of electrons circling the atomic nucleus like little planets did not fit the new data physicists were gathering. But unlike Heisenberg’s purely mathematical approach, Schrödinger proposed a new theory that replaced orbiting electrons with an image more like standing waves around the nucleus – waves like those found in a plucked guitar string or the head of a beaten drum. By applying an existing mathematics of wave functions to atomic questions, Schrödinger was able to create equations that matched the properties of simple atoms.

“It became clear during the months of Pauling’s stay in Europe that Schrödinger’s and Heisenberg’s ideas were not two different realities but two different mathematical methods for arriving at the same atomic reality. Ultimately they became joined under a new name: quantum mechanics. Researchers, it seemed, could pick whichever method was easiest to use for a particular problem. Pauling preferred the wave approach not only because the mathematics was somewhat easier for him but also, he said, because it contained ‘at least a trace of physical picture behind the mathematics.’

"Linus Pauling returned to America in 1927 fired with the inspiration of the new quantum mechanics. He was one of the first Americans to understand the importance of the European revolution in physics, and one of the first to apply its lessons to the field of chemistry” (scarc.library.oregonstate.edu/coll/pauling/bond/index.html).

Pauling was building on a body of earlier work regarding the use of quantum physics to study chemical structure, most notably a 1927 paper by Walter Heitler and Fritz London. Also, parts of his work were independently duplicated by J. C. Slater, thus leading to the name HLSP (Heitler-London-Slater-Pauling) theory, which Pauling used in his own writing to refer to the valence bond theory. While Heitler and London’s contributions are frequently highlighted in European writing on the subject, Americans, particularly chemists, tend to associate the theory primarily with Pauling. But the truth is that, while Heitler and London's work was important, Pauling was the first to devise a systematic method for applying quantum-mechanical concepts to complex molecules. It was Pauling's ideas that made the crucial link between the atomic and molecular realms.

“It is perhaps difficult for the nonscientist to appreciate the magnitude of this achievement. Even a molecule as ‘simple’ as methane, considered as a system of elementary particles, was far too complex to be analyzed mathematically using the equations of quantum physics. One might say that deriving the behavior of a molecule by quantum physics is like deriving the behavior of a group of people from a knowledge of the personalities of the individual people. In both cases, certain rough predictions can be made easily, but gaining detailed understanding is very difficult, because many subtle interactions are at play.

“Today one can obtain rather good results about molecular structure from computer simulations, but in the 1920s and 1930s computers did not exist, and one had to rely entirely on human ingenuity and mathematical tables. Pauling’s theory of the chemical bond consisted of six rules, three of which followed fairly directly from the mathematics of quantum theory as applied to hydrogen, helium, and lithium atoms, and three of which were pure inspiration. Each of these rules was stated in mathematical form. It is possible, however, to express the meaning of the rules in ordinary language, although much of the precision is lost.

“The first three rules, roughly speaking, are as follows: First, electron­pair bonds are formed by the interaction of two unpaired electrons, one on each of the two bonding atoms. Second, the spins of the electrons must be opposed when the bonds are formed, so that they do not contribute to the magnetic properties of the substance. And third, the two electrons that form a shared pair cannot take part in forming additional pairs. These rules systematized the understanding of chemical bonding that was emerging from the rapidly developing quantum theory.

“The next three rules were fundamentally novel; they may represent Pauling’s greatest stroke of genius. They exemplify, more than any other single discovery, the extraordinary chemical intuition that, in one area after another, led Pauling to simple and elegant explanations of extremely complex phenomena. The rules were justified, in the 1931 paper, by sketchy mathematical and qualitative arguments; their real justification lies in the numerous chemical structures that have been correctly inferred from them.

“The fourth rule states that the most important terms in the equations for the electron-pair bond are those involving only one quantum wave function from each atom. This is a mathematical approximation of the type often made by physicists: one ignores interactions that are ‘small’ in magnitude in order to derive tractable equations. The trick is always to make the right approximation – not to overlook the important points. Pauling’s fourth rule was inspired by the nineteenth-century idea of valence; it was ‘right’ in the sense that the interactions that it ignored were in many cases insignificant.

“Pauling’s fifth rule was the greatest innovation: it states that, generally speaking, stronger bonds are formed by orbitals that overlap more with orbitals of the other atom. So, if there are two orbitals competing for a bond with a certain atom, the winner will be the one that overlaps more with that atom. In addition, the direction of the bond formed by an orbital will tend to be the same as the direction that the orbital is concentrated in. There was nothing in the old idea of valence to suggest this fifth rule, because the idea of ‘overlap’ was a new one, a corollary of the idea of a quantum wave function. However, despite its lack of precedents, the rule smacks of common sense. Greater overlap makes a stronger bond, and the bond is in the direction of the orbital that is bonding – these are very natural, intuitive conclusions.

“Finally, the sixth rule states that, between two orbitals concentrated in approximately the same direction, the stronger bonds will be formed by the orbital closer to the nucleus of the atom, which corresponds to a lower energy level for the atom. This rule is mathematically similar to the fifth rule but tends to have fewer direct applications.

“The fifth rule implies … the hybridizationof orbitals – the ability of bonding, in itself, to affect the form taken by the orbitals of an atom. If one wished to wax poetic, one might say that atoms reach out to each other, distorting the quantum wave functions of their electrons in precisely the most effective way to ‘grab’ each other. In this way atoms join together to make molecules, the basic elements of matter. This is a natural, intuitive idea, almost visceral in its simplicity, and it cuts through the complexity of interacting quantum wave functions in a most remarkable way.

“This work culminated in a series of important papers, beginning with ‘The Nature of the Chemical Bond’ in 1931 [the offered paper], and is described in detail in Pauling’s book The Nature of the Chemical Bond (1939). The pivotal concept in the theory is the highly technical, highly innovative idea of the hybridization of orbitals, based on the concept of resonance among different electrons.

“The basic idea for this paper came to Pauling in a flash of insight, after many days of struggling with complex mathematical models:

‘Finally, in December 1930, one day I thought of a way to get around the mathematical difficulties. A simplification which made it very easy to get the results. And 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 and get the answer and solve another equation … I just kept getting more and more euphorious as time went by, and it didn't take me long to write a long paper about the nature of the chemical bond. That was a great experience.’

“The 1931 paper combined chemistry and physics to an unprecedented extent. And, years later, Pauling remembered believing that it would have the journal editor, Arthur Beckett Lamb,

‘buffaloed … [He] thought, ‘What referee shall I send this paper to? It has to be somebody who has a good knowledge of chemistry … but also has a thorough understanding of quantum mechanics, and I can’t think of anybody of that sort,’ anybody who might be said to be my peer. He [thought], ‘Well, past experience has shown that this author knows what he's writing about, so I'll just go ahead and publish the paper.’

“The paper appeared just seven weeks after it was submitted. The original 1931 article was followed within the next three years by many other articles refining and developing Pauling’s model of the chemical bond and applying it to numerous other substances. Pauling’s achievement was quickly recognized by the scientific establishment in the United States. Late in the spring of 1931, he was selected to receive the Langmuir Prize from the American Chemical Society. He was the first recipient of this award, which was intended to honor the most promising young research chemist in the United States. Overnight, Pauling became a celebrity. His office and his home were invaded by reporters. Caltech and Pasadena were proud of the accomplishments of one of their favorite sons. The wire services spread the news throughout the country and abroad. The New York Times and Herald Tribune, the Christian Science Monitor, The Nation, and the Portland Oregonian were among the publications that spoke of Pauling as ‘the rising star who may yet win the Nobel Prize.’ They were quoting the president of the American Chemical Society.

“The New York Times told how Albert Einstein, while visiting the Pasadena campus in 1931, asked many questions of Pauling at a seminar, confessed his lack of understanding of the chemical bond, and apologized for taking so much of the speaker’s time. The Portland Oregonian speculated that if only ten men in the world could understand Einstein’s theory of relativity, there must be even fewer who could understand Pauling’s work. This was not actually true of Pauling’s or Einstein’s work, of course. Pauling’s work was readily understood by other specialists in the field of molecular chemistry. In fact, unlike many other leading scientists, Pauling had a great gift for making his ideas intelligible and did so frequently in lectures” (Goertzel & Goertzel, pp. 72-77).



Offprint from: Journal of the American Chemical Society, Vol. 53, April 1931. 8vo (218 x 140 mm), pp. 1367-1400. Stapled as issued in self-wrappers. A very fine copy.

Item #4772

Price: $15,000.00

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