Gilbert Newton Lewis(1875-1946): Master of physical chemistry

GILBERT NEWTON Lewis was born on October 25, 1875 in West Newton, Massachusetts (U.S). He was educated at home by his parents. He read at the age three and was intellectually precocious. He was enrolled in the preparatory school at Nebraska when he was 14. After two years' study at the University of Nebraska, he shifted to Harvard University, where he took the B.S. Degree in 1996. He did research work on electrochemical potentials under T. W. Richards and obtained his Ph.D in 1899. He then proceeded to Germany, the center of physical chemistry and studied with Nermst at Goettingen and with Ostwald at Leipzig. Upon his return to Harvard 1901, he was appointed instructor in thermodynamics and electrochemistry. Out of the thermodynamic relations known in 1895 as isolated equations he evolved a logical system from which, given one relation, the rest could be derived. He proposed the new idea of escaping tendency (which he called fugacity), namely the tendency of a substance to pass from one chemical phase to another.

Lewis career was spread among three famous institutions, namely Harvard (1901-05) M.I.T (1905-12) and University of California Berkley (1912-46). Most of his research interests originated during the Harvard period. He was disappointed that his talents were not appreciated. He refused an invitation in 1928 and an honorary degree in 1929 from Harvard.

Free energy and entropy

Most chemists relied on the familiar thermodynamic science of the calirometric school (Berthelot, Ostwald and Vant Hoff). Heat of reaction alone is not a measure of the tendency of chemical changes to occur. Lewis proposed that only free energy and entropy could provide an exact chemical thermodynamics. Much of his career was devoted to making these useful concepts accessible to practical chemists.

Lewis found existing free-energy data unreliable, contradictory; and existing methods for measuring free energies imperfect. At M.I.T he systematically studied the free energy of formation of compounds of Oxygen, nitrogen, the halogens, sulfur and the alkali metals.

In 1907 Lewis formulated a new system of thermodynamics based on the ``concept of activity,'' a function which expresses the tendency of substances to cause change in chemical systems. He further showed that in terms of activity, all standard thermodynamic equations for ideal systems became ``perfectly exact and general'' for real systems. Lewis main contribution to thermodynamics was not in grand theory but in its practical applications to real systems.

During 1913 to 1920, Lewis published a series of lengthy papers - many in collaboration with Randall - collecting and reworking the free- energy data of each element, a compendium of entropy data, and an empirical verification of Nernst's third law. All this material became the body of his book Thermodynamics and Free Energy of Chemical Substances (1923).

Valence theory

Early in 1916, Lewis proposed that the chemical bond was a pair of electrons shared or held jointly by two atoms. Interms of cubic atoms, the single bond was represented by two cubes with a shared edge. From this simple idea Lewis derived structures for the halogen molecules, the ammonium ion, and the oxyacids, all of which proved insoluble for previous theories of valence. Lewis conceived polar bonds simply as unequally shared electron pairs.

Lewis' theory of the shared-pair bond received no notice in 1916. His `static' atom appeared to be inconsistent with the physicists' view of the atom which demanded moving electrons, as in Bohr's planetary model. The `dynamic' atom failed to explain the rigid stereo-chemistry of carbon compounds.

Lewis vigorously defended the static atom against Bohr's atom in a lecture to the Faraday Society and in his book Valence and the Structure of Atoms and Molecules (1923).

The conflict between the static and dynamic atoms soon disappeared. But the shared-pair bond proved to be one of the most fruitful ideas in the history of chemistry. The chemical bond became more than a simple line.

In the late 1920's the shared electron pair bond apparently triggered the birth of the new quantum chemistry. The work of Schroeduinger, London and Pauling transformed Lewis' germinal idea into a quantum mechanical theory of molecular structure.

With the publication in 1923 of the book Thermodynamics and the Free Energy of Chemical Substances in collaboration with M.Randall, thermodynamics - once regarded as the luxury of specialists, became an indispensable part of chemical engineering education.

Theory of radiation

Lewis ended his work in 1923 on the two of his most abiding interests already discussed and occupied himself (1922-33) with his third interest, the theory of radiation and relativity. He tried to derive the laws of quantum radiation by thermodynamic reasoning. He met entrancing paradoxes of space and time, which resulted in his book The Anatomy of Science (1926).

The profound revolution in physics in the 1920's brought down some cherished beliefs, which he sensed. So he abruptly abandoned theorizing to enter a field quite new to him, the separation of isotopes.

Deuterium had been discovered (1932) by Harold Urey who noted it might be isolated on a large scale by fractional electrolysis of water. Lewis brought out 28 reports on deutreium chemistry. He foresaw a whole new chemistry of deutro compounds which showed potential for studying organic and biochemical reactions.

Finally Lewis hit upon (1938) a fruitful combination of theory and experiment in photochemistry. He had long been interested in the theory of colored compounds. His idea of the shared-pair bond led him to propose (1916) that colour was due to the presence of ``odd'' electrons. This won him Nichols Medal in 1921.

According to his generalized theory of acids and bases (1923), bases were molecules having free electron pairs whereas acids were molecules that could accept an extra electron pair. He published his ideas in the paper. Acids and Bases (Journal of the Franklin Institute, Vol226, 1938).

Lewis died on March 23, 1946 at Berkeley, while carrying out an experiment on fluroscence. (The Dictionary of Scientific Biography, Ch. Scribner's sons, New York).

R.Parthasarathy

Send this article to Friends by E-Mail

Section  : Science & Tech
Previous : Question Corner
Next     : Within sight of cyber cinema