He also had the great pleasure of seeing several of his close associates receive their own Nobel Prizes, including Rutherford in chemistry (1908) and Aston in chemistry (1922). Thomson received various honors, including the Nobel Prize in Physics in 1906 and a knighthood in 1908. In 1913 Thomson published an influential monograph urging chemists to use the mass spectrograph in their analyses. His nonmathematical atomic theory-unlike early quantum theory-could also be used to account for chemical bonding and molecular structure (see Gilbert Newton Lewis and Irving Langmuir). Otto Hahn, who later discovered atomic fission, worked under Rutherford at the Montreal Laboratory in 1905-06. Of all the physicists associated with determining the structure of the atom, Thomson remained most closely aligned to the chemical community. The theory was supported by a large amount of experimental evidence, a number of new radioactive substances were discovered and their position in the series of transformations was fixed. He was a good lecturer, encouraged his students, and devoted considerable attention to the wider problems of science teaching at university and secondary levels. Even though he was clumsy with his hands, he had a genius for designing apparatus and diagnosing its problems. In 1884 he was named to the prestigious Cavendish Professorship of Experimental Physics at Cambridge, although he had personally done very little experimental work. He was then recommended to Trinity College, Cambridge, where he became a mathematical physicist. Instead young Thomson attended Owens College, Manchester, which had an excellent science faculty. His father intended him to be an engineer, which in those days required an apprenticeship, but his family could not raise the necessary fee. The neutron had not yet been discovered when Rutherford proposed his model, which had a nucleus consisting only of protons. Ironically, Thomson-great scientist and physics mentor-became a physicist by default. Physicist Ernest Rutherford envisioned the atom as a miniature solar system, with electrons orbiting around a massive nucleus, and as mostly empty space, with the nucleus occupying only a very small part of the atom. His assistant, Francis Aston, developed Thomson’s instrument further and with the improved version was able to discover isotopes-atoms of the same element with different atomic weights-in a large number of nonradioactive elements. Here his techniques led to the development of the mass spectrograph. Thomson’s last important experimental program focused on determining the nature of positively charged particles. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved. In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. Structure of the Atom and Mass Spectrography
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