Abstract
THE fact that the same element may exist in two or more forms, which are chemically identical even though their atomic weights differ, was first noted by Soddy (1910) in connexion with radioactive elements. A little later Sir J. J. Thomson (1913) showed, by the method of positive ray analysis, that neon, with an average atomic weight of 20-2, is a mixture of two kinds of atoms with masses 20 and 22 respectively. The brilliant extension of this method of attack by Aston established that most of the common elements are similarly inhomogeneous. Chlorine (35-457) is a mixture of 35C1 and 37C1 ; tin (118-70) exists in as many as ten forms, with atomic masses ranging from 112 to 124. These chemically identical species of the same element with diverse masses are known as isotopes.
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KENDALL, J. SEPARATION OF ISOTOPES AND THERMAL DIFFUSION*. Nature 150, 136–140 (1942). https://doi.org/10.1038/150136a0
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DOI: https://doi.org/10.1038/150136a0
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