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Soddy, Frederick

atomic atoms helium chemical

(1877–1956) British radio-chemist; proposed theory of radioactive decay (with Rutherford); pioneer theorist and experimenter in radiochemistry.

The youngest of seven children, Soddy grew up to become a forceful, talented and eccentric individual. After graduating in chemistry from Oxford, he found a job as demonstrator at McGill University in Montreal. was there as professor of physics, and his work needed a chemist. Together during 1900–03 they offered a brilliant and simple answer to the question: what is radioactivity? Their disintegration theory proposed that heavy atoms are unstable; that such an element could undergo spontaneous atomic disintegration, losing some mass and charge from its atoms and forming a new element. The process could recur, so that a series of such changes occurred. They went on to predict that helium gas should be a decay product of radium. In 1903, working with in London, Soddy used 52 mg of radium bromide, collected gas from it and showed this to contain helium.

In 1913, Soddy gave the clearest of the statements of the radioactive displacement law that emerged about that time: that emission of an alpha-particle (helium nucleus) from an atom reduces its atomic number by two; whereas the emission of a beta-particle (an electron) increases the atomic number by one.

It was Soddy who gave the name ‘isotopes’ to atoms with the same atomic number (and therefore the same chemical properties) but differing in mass. In 1920 he foresaw their value in finding the age of rocks; back in 1906 he had foreseen the use of atomic energy from uranium, which he also lived to see (1945). In 1919 he was appointed professor in Oxford. He was frustrated there in his efforts to change chemical teaching and research arrangements, and his interest in chemistry faded after his Nobel Prize award (1921). His new concern was for political and economic schemes which would ensure that the benefits of science became widely available, but he was unsuccessful as an advocate for his ideas.

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