edited bv ROGER R. FESTA Schml oi Education. Box U-33 The University of Connecticut Storrs, CT 06268
Frederick Soddy: From Alchemy to Isotopes Miriam C. Nagel Awn High School Avon, CT 06001
In 1921 the Nobel Prize in chemistry was awarded to Frederick Soddy "for his contributions to the knowledge of the chemistry of radioactive substances and his investigations on the occurrence and nature of isotopes!' 1 The youngest son of a prosperous merchant, Frederick Soddy was the first in his family to follow a career in science. He was born September 2,1877, in Easthourne, a small city on the Enelish Channel. The Soddv familv followed the tenets of ~ a l v k s mand , the boy was indoctrinated in the importance of truthfulness. sohrietv. industrv. and resnonsihilitv. Soddy became interested in chemistry w h e attending the Eastbourne schools. By 1896 he was an undergraduate a t Oxford where he was active in the Junior Chemical Society. Amone his scientific interests was transmutation. the historicacgoal o i the alchemists. He graduated with first honors in 1898 but remained at Oxford until thesummerof 1900 when he went to Canada. After a~olvine. . . . .. unsnccessfullv. .. for a iob in Toronto. Soddv went to Montreal where he visited the impressive chemical laboratories at Mr(;ill Universitv. He was hnunv to find a ioh there as a demonstrator (lab i&tructor). ~ t ' t L esame time, Ernest Rutherford.. six vears Soddv's senior and a ohvsics . . . professor at MrGill, needed a chemist to nssiat in his investieati(ms of radioactivitv. Shortlv after atmtinr! work at MrCill. &idy said, " ~ u t h e r f i r d. . . me. I ahandined all to follow him, and for more than two vears scientific life became hectic to a degree rare in the lifetime of an individual." 2 Although both men had forceful personalities, their shared interest in radioactivity made for a successful collaboration. They complemented each other, the superb physicist and the exceptionally skilled research and theoretical chemist. Early in their research, they assigned to astudent the task of measuring the radioactivity of a sample of thorium with an m widely to be useful. electroscope. His measurements varied t Some detective work indicated the intensity was greatest when the lab door was closed, least when i t was open. After pondering the strange results, Rutherford and Soddy discovered that a radioactive gas was being produced by the thorium. When the door was shut, the gas stayed near the source, adding to the reading on the electroscope. When the floor was open, drafts quickly dispersed the gas.%They used liquid air to condense some of the gas which Soddy described as "a sort of continuous snowstorm silently going on covering every available surface with this invisible, unweighahle hut intensely radioactive denosit!' 3 I t took much more investigating to discover that the gas was not ~roduceddirectlv bv thorium. An intermediate substance was-involved. odd; discovered irregularities between the radioactivity of thorium hydroxide and thorium carhonate.
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New York Times, Sept. 23, 1956, p. 85, col. 1. ZCline. Barbara Loven, "The Questioners: Physicists and the Quantum Theory." Thomas Y. Crowell Co., New York, 1965, p. 20. Weeks, Mary Elvira. ''The Discovery of the Elements." Chemical Education Publishing Co., Easton, PA, 1934, p. 301. Williams, T. I., Endeavour, 23, 54 (1964).
He prepared a thorium nitrate solution and divided i t in half, precipitating the hydroxide in one half and the carbonate in the other. The solid hydroxide was separated hy filtration and the filtrate evaporated. The hydroxide was highly radioactive. surprisingly, even the residue from the filtrate was also emitting. But when he separated the solid carbonate, he found that it showed little radioactivity. Soddy and Rutherford suspected the thorium was contaminated with thorium X, a suhstance recently described by William Crookes in London. Results still indicated the presence of thorium X when the tests were reneated with nure thorium nitrate. Careful measurements over a period o i time and evidence of the tests convinced Frederick Soddy that some new and chemically different substances were being evolved. He and Rutherford checked the eilecrs of temoerature and variations in solution conditions to see if their results could be tied to a chemical change, but the rate of production of new matter was unaffected. In 1902, Rutherfor4 and Soddy announced a revolutionarv new theorv that "radioactivitv is a t once an atomic phenomenon and the accompaniment of a chemical change in which new kindsof matter are oroduced." "Soddv usedihe alchemists' term transrnutntiin to describe their theorv. ~ G i o uabout s the gases also emanating from radium, Soddy left Rutherford in March 1903, t o work in London with Sir William Ramsay who had eqlier discovered the family of inert cases. Soddv's first concern was to locate a s u-. n ~-l vof nure radium for his investigations. Soon after his arrival, he chanced on uure radium bromide on sale in a shoo a t seven shillings andsix pence a milligram. "Even I could Gford some a t this price and I a t once ordered 20 milligrams," Soddy recorded. "With this 20 mg, and a separate hatch of 32 mg . . . lent by Rutherford," 4 Soddy and Ramsay proved through spectroscopic studies on July 8, 1903, that helium gas was a nroduct of radioactive decav. Soddv concluded that the heli;m originated as alpha paiticles. i n 1908, Rutherford confirmed Soddy's theory. Soddy also identified the mysterious radioactive gas produced by thorium and radiumas another inert gas. I t is now known as radon-220. After his productive year with Ramsay and a lecture tour in Australia, Frederick Scddy became a lecturer on physical chemistry a t the University of Glasgow in the fall of 1904. During the next six years he continued his experiments in radiochemistry, including work on the purification of radioactive materials. In 1910 while extracting mesothorium chloride, he discovered that he was also getting radium chloride and the chloride of thorium X from the uranium in his sample. After carefully evaluating his results, Soddy concluded that mesothorium, radium, and thorium X were chemically identical. Early in 1912, he invited a young Glasgow chemist, Alexander Fleck, to work with him in determining the chemical properties of the recognized radioactive intermediates. They discovered more chemically identical, short-lived radioactive elements. Some were chemicqlly inseparable and spectroscopically
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"Profliesin Chemisw' is a biographical feature. highlighting the conblbutions of distinguished chemists in the context of their lives. The column is designad for curriculum enrichment,allowing the secondav school teacher to enhance the vitality of chemistry pith the sense of scholarship end adventure shared by chemists throughout history.
Volume 59
Number 9
September 1982
739
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identical hut, curiously, disintegrated in different ways. Soddy brought order to the confusion when he advanced his general displacement law in 1913. He recognized that when an alpha particle was expelled, an element shifted two places in the direction of lower mass on the periodic table; then loss of two beta particles would return the element to its original position. When the element was hack in its "same place" on the periodic table, i t would be the same element it was originally, chemically and spectroscopically, hut its weight would he different. At a dinner party given by his father-in-law, an industrial chemist, a discussion of Soddy's novel concept led a family friend, Dr. Margaret Todd, to suggest the name isotope (from the Greek, isos topos, meaning "same place") for atoms chemically identical hut having different weights.
740
Journal of Chemical Education
In 1919, Frederick Soddy h e m e professor of inorganic and physical chemistry at Oxford. Two years later he was awarded the Nobel Prize. Although credited with working to improve the quality of chemistry teaching and modernizing the lahoratories at Oxford, Soddy turned much of his attention to publicizing his unorthodox theories on economics which never became popular. Following his wife's death, he retired from Oxford in 1936. After World War 11, Soddy openly spoke out for greater control of atomic weapons. He joined seventeen other Nobel Prize-winning scientists in July 1955 in warning of the dangers of contamination from nuclear explosions. Soddy died on September 21, 1956, in Brighton, not far from his birthplace. He was 79 years old.
