SIDGWICK, NEVIL VINCENT

(b. Oxford, England, 8 May 1873; d. Oxford, 15 March 1952)

Chemistry.

Sidgwick was born into a family of unusual distinction. His father, William Carr Sidgwick, was a fellow of Merton College, Oxford. His uncles included Henry Sidgwick, professor of moral philosophy at Cambridge; Arthur Sidgwick, reader in Greek at Oxford; and (by marriage) Edward White Benson, archbishop of Canterbury. From them he may well have inherited or absorbed his power of mental organization and his command of language. Until he was twelve years old Sidgwick was educated at home, mainly by his mother, Sarah Isabella Thompson, F.R.S., and it was to her that he owed his introduction to botany and natural history and his general love of science.

Sidgwick went Rugby School when he was thirteen and, unusually for that time, studies both the classics and science. In 1892 he returned to Oxford as a scholar of Christ Church. His tutor was Vernon Harcourt, a pioneer in reaction kinetics. Sidgwick earned a first-class degree in chemistry in 1895. Then, reputedly because of a disparaging remark by a relative about science, he studied literae humaniores and gained a brilliant first in 1897, largely by his performance in philosophy. Next he went to Germany, where he studied physical chemistry under Georg Bredig in Ostwald’s laboratory at Leipzig and then organic chemistry with Hans von Pechmann at Tübingen.

In 1900 Sidgwick was elected a fellow of Lincoln College, Oxford, and there spent athe rest ot his working life. Until 1920 he had published only eightreen papers. Most of these were concerned with the kinetics of organic reations, the others mainly with the relation of solubility and chemical structure. These papers described good, careful work; but none was of great importance. He would have been unknown outside Oxford had he not written Organic Chemistry of Nitrogen (1910). This was his first essay in applying the ideas and quantitative methods of physical chemistry to the facts and systematics of descriptive chemistry, a task that gradually became his major interest. The book was a great success, not only because of his shrewd selection of topics and his clarity of thought but also because of the intellectual excitement conveyed by his style.

From 1920 Sidgwick’s rate of publication increased rapidly, probably because the introduction of a year or research as a part of the chemistry course provided him with more research pupils. His major accomplishement was establishing that there can be a definite bond between a group containing a fairly acidic hydrogen atom (for example, hydroxyl group) and an oxyten-rich group (for example, nitro group). Such a bond via a hydrogen atom had already been postulated by various people; but the clear, systematic attack by Sidgwick and his pupils played a major part in gaining general eral acceptance of the idea. He was elected a fellow of the Royal Society in 1922.

In 1914, while traveling to Australia for a meeting of the British Association, Sidgwick met Ernest Rutherford and immediately came under his spell. This friendship was of crucial importance, for it inspired Sidgwick to try to explain chemical behavior in terms of atomic structure, as G. N. Lewis and Langmuir were also doing. The first major fruit of this new interest was the publication in 1927 of Electronic Theory of Valency, which was intended as an exposition of principles to be followed by a second volume applying them systematically. One of the most novel and important parts of this book was that concerned with the coordination compounds or complexes so extensively studied by A. Werner. Sidgwick showed that, by using the concept of the dative bond (Wherein both bonding electrons are provided initially by one of the two atoms involved, instead of one by each), it is possible to rationalize these compounds more successfully than had been done previously. Lewis had already put forward the concept of this bond, but it was Sidgwick’s systematic application of the idea that made chemists realize its value and wide importance. Sidgwick also emphasized that both ionic and covalent bonds exist, that generally they are sharply distingusished, and that a given bond might exist in either form, for example, when an acid ionizes. The book presented a brilliant discussion of a wide range of topics on a simple basis, and it had a profound effect.

Even as the book was written, however, the theorectical basis that Sidgwick had used, namely, the quantum menchanics of Bohr, Sommerfeld, and W. Wilson, was being discarded by physicists in favor of a much more general mechanics formulated in matrix form by W. Heisenberg and as a wave equation by Schrödinger. In 1927 W. Heitler and F. London produced an explanation of the covalent bond that was far more fundamental than anything previously advanced. A year later F. Hund produced an alternative treatment. Both theories were quickly taken up and developed. From the former, J.C. Slater and L. Pauling derived, in the early 1930’s, a basis for stereochemistry; and they also introduced the concept of “resonance” in molecules; electrons holding a set of atoms together may be more generally distributed of “declocalized,” so that each electron can be considered to play a part in holding several atoms together. From Hund’s explanation R.S. Mulliken and E. Hückel developed an alternative treatment for many-atom molecules, the “molecular orbital” method.

Sidgwick went to the United States for the first time in 1931, as George Fisher Baker nonresident lecturer in chemistry at Cornell University, and in his travels met Pauling. They immediately became fast friends. Thereafter one of Sidgwick’s main preoccupations was to expound the concept of resonance to British chemists. He did so in various articles and in his presidential addresses to the Chemical Society (1936, 1937). He had a flair for extracting the essence of a mathematical argument and expressing it verbally.

Sidgwick had become embarrassed by the success of his books. There had long been a demand for a new edition of his book on nitrogen compounds. Twenty-five years after publication secondhand copies were selling for four times the original price. But realizing that he could not prepare a new edition, he had his colleagues T. W. J. Taylor and W. Baker take over the task and prepare a reworked edition in 1937. Another edition was produced in 1966 by I. T. Millar and H. D. Springall. To meet the requirements of his Cornell appointment Sidgwick published Some Physical Properties of the Covalent Link in Chemistry (1933), which dealt mainly with the new experimental methods for investigating structure, such as heats of formation, lengths, and electric dipole moments of bonds. Because of its relatively limited scope, it did not have the importance of the book on valence theory.

Sidgwick then began writing volume II of his Electronic Theory of Valency. Curiously, the hardships created by World War II may have helped Sidgwick to complete this task, the size of which became clearer and more daunting as he proceeded. The limitations on travel meant fewer outside demands on his time: and still more important was the diminution in the world output of primary publications. He consulted 10,000 papers, mostly on his own but also with help from H. M. Powell and R. V. G. Ewents. Eventually, in 1950 when he was seventy-seven, the work appeared as Chemical Elements and Their Compounds, two large volumes of about 750,000 words. While it did not have the impact of volume I, it was still a landmark in the development of chemistry. Once again he had brought unification, this time to an even vaster body of fact. His clear critical mind and easy style illuminate every word. Although the book has become dated it still is a prime source of earlier references. The emphasis by chemists on the molecular orbital method began just as his writing finished. In the 1950’s the ligand field treatment of complexes was developed at Oxford by L. E. Orgel, a pupil of a pupil. Accurate determinations of geometric structures of molecules began to pour forth after 1945. Completely unforeseen developments occurred, notably in the discovery of new organometallic compounds and of compounds of the once inert gases.

Today it is impossible for a large book about descriptive chemistry to remain in date for more than a few years after it is started; and no satisfactory technique for dealing with this situation has yet been devised. What is certain is that no one man can ever again attempt such a task with any hope of being effective: thus Sidgwick may be regarded as the last of a line. He showed shrewdness, or had luck, in applying his talents when they were particularly useful in the development of chemistry.

Sidgwick did not live long enough to enjoy his final success. His health had been slowly failing for more than ten years, and he had completed his writing only because of his indomitable will. But he was able to achieve again his dearest ambition, to revisit the United States, to meet his old friends, and to see the beauty of New England in the fall. On the return voyage he collapsed aboard ship. He was brought back to Oxford, where he died in his sleep.

Sidgwick’s influence on those who knew him was as much due to his personality as to his writings. He never married, although he enjoyed the company of women–provided that they were intelligent. He lived in college–very simply save when he entertained. He was a generous and genial host, delighting in lively discussions and pungent repartee.

BIBLIOGRAPHY

I. Original Works. A complete bibliography is given by Tizard (see below). Sidgwick’s books are Organic Chemistry of Nitrogen (Oxford, 1910); Electronic Theory of Valency (Oxford, 1927); Some physical Properties of the Covalent Link in Chemistry (Ithaca, N. Y., 1933); and Chemical Elements and Their Compounds, 2 vols. (Oxford, 1950).

II. Secondary Literature. The most helpful source is Sir Henry Tizard’s article in Obituary Notices of Fellows of the Royal Society of London, 9 (1954), 237–258. with bibliography. See also L. E. Sutton’s obituary in Proceedings of the Chemical Society (1958), 310–319.

L. E. Sutton