Urey Discovers Deuterium and “Heavy Water” (Great Events: 1900-2001)
Article abstract: Harold Urey isolated and identified deuterium, thus establishing the existence of rare isotopes in elements.
The Question of Atomic Weight
Atoms are generally composed of three particles: protons, neutrons, and electrons. The periodic table of elements ranks elements according to the number of protons they contain. Thus, hydrogen has the atomic number 1 because it has only one proton in its nucleus, whereas uranium has the atomic number 92 because it has ninety-two protons in its nucleus. “Species” that have the same number of protons but different numbers of neutrons have the same name and occupy the same position in the periodic table. Such species are called “isotopes,” a term that comes from the Greek words iso, meaning same, and topos, meaning space.
The concept of isotopes was first introduced in 1913 by Frederick Soddy, who provided evidence that different elements can occupy the same position in the periodic table. In the early 1920’s, Francis William Aston determined that the atomic weight of hydrogen was one-sixteenth that of oxygen. This value did not have to do with isotopes; it had to do with the fact that hydrogen has one proton, no neutrons, and no electrons, whereas oxygen has eight protons, eight neutrons, and eight electrons. After Aston made this determination, William Francis Giauque discovered the existence of oxygen isotopes that had more...
(The entire section is 1119 words.)
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