Gilbert Newton Lewis ForMemRS (October 23, 1875 – March 23, 1946) was an American physical chemist known for the discovery of the covalent bond and his concept of electron pairs; his Lewis dot structures and other contributions to valence bond theory have shaped modern theories of chemical bonding. Lewis successfully contributed to thermodynamics, photochemistry, and isotope separation, and is also known for his concept of acids and bases. G. N. Lewis was born in 1875 in Weymouth, Massachusetts. After receiving his PhD in chemistry from Harvard University and studying abroad in Germany and the Philippines, Lewis moved to California to teach chemistry at the University of California, Berkeley. Several years later, he became the Dean of the college of Chemistry at Berkeley, where he spent the rest of his life. As a professor, he incorporated thermodynamic principles into the chemistry curriculum and reformed chemical thermodynamics in a mathematically rigorous manner accessible to ordinary chemists. He began measuring the free energy values related to several chemical processes, both organic and inorganic. In 1916, he also proposed his theory of bonding and added information about electrons in the periodic table of the elements. In 1933, he started his research on isotope separation. Lewis worked with hydrogen and managed to purify a sample of heavy water. He then came up with his theory of acids and bases, and did work in photochemistry during the last years of his life. In 1926, Lewis coined the term "photon" for the smallest unit of radiant energy. He was a brother in Alpha Chi Sigma, the professional chemistry fraternity. Though he was nominated 35 times, G. N. Lewis never won the Nobel Prize in Chemistry. On March 23, 1946, Lewis was found dead in his Berkeley laboratory where he had been working with hydrogen cyanide; many postulated that the cause of his death was suicide. After Lewis' death, his children followed their father's career in chemistry. In 1908 he published the first of several papers on relativity, in which he derived the mass-energy relationship in a different way from Albert Einstein's derivation. In 1909, he and Richard C. Tolman combined his methods with special relativity. In 1912 Lewis and Edwin Bidwell Wilson presented a major work in mathematical physics that not only applied synthetic geometry to the study of spacetime, but also noted the identity of a spacetime squeeze mapping and a Lorentz transformation. In 1913, he was elected to the National Academy of Sciences. He resigned in 1934, refusing to state the cause for his resignation; it has been speculated that it was due to a dispute over the internal politics of that institution or to the failure of those he had nominated to be elected. His decision to resign may have been sparked by resentment over the award of the 1934 Nobel Prize for chemistry to his student, Harold Urey, for the discovery of deuterium, a prize Lewis almost certainly felt he should have shared for his work on purification and characterization of heavy water. Lewis was the first to produce a pure sample of deuterium oxide (heavy water) in 1933 and the first to study survival and growth of life forms in heavy water. By accelerating deuterons (deuterium nuclei) in Ernest O. Lawrence's cyclotron, he was able to study many of the properties of atomic nuclei[citation needed]. During the 1930s, he was mentor to Glenn T. Seaborg, who was retained for post-doctoral work as Lewis' personal research assistant. Seaborg went on to win the 1951 Nobel Prize in Chemistry and have the element seaborgium named in his honor while he was still alive. On June 21, 1912, he married Mary Hinckley Sheldon, daughter of a Harvard professor of Romance languages. They had two sons, both of whom became chemistry professors, and a daughter.