Abstract
II
The Periodic Law and Radio-active Change.
THE second line of advance interprets the periodic law. It began in 1911 with the observation that the product of an a-ray change always occupied a place 4n the periodic table two places removed from the parent in the direction of diminishing mass, and that in subsequent changes where a rays are not expelled, the product frequently reverts in chemical character to that of the parent, though its atomic weight is reduced four units by the loss of the a particle, making the passage across the table curiously alternating. Thus the product of radium (Group II.) by an a-ray change is the emanation in the zero group, of ionium (Group IV.) radium. and so on, while in the thorium series thorium (Group IV.) produces by an a-ray change mesothorium-I (Group II.), which in subsequent changes in which no a rays are expelled yields radio- thorium, back in Group IV. again ( Chemistry of the Radio-Elements, p. 29, first edition, 1911). Nothing at that time could be said about /3-ray changes. The products were for the most part very short-lived and imperfectly characterised chemically, and several lacuna still existed in the series, masking the simplicity of the process. But early in 1913 the whole scheme became clear, and was pointed out first by A. S. Russell, in a slightly imperfect form, independently by K. Fajans from electrochemical evidence, and by myself in full knowledge of Flecks results, still for the most part unpublished, all within the same month of February. It was found that, making the assumption that uranium-X was in reality two successive products giving /3 rays, a prediction Fajans and Gohring proved to be correct within a month, and a slight alteration in the order at the beginning Of the uranium series, every a-ray change produced a shift of place as described, and every /3-ray change a shift of one place in the opposite direction. Further, and most significantly, when the successive members of the three disintegration series were put in the places in the table dictated by these two rules, it was found that all the elements occupying the same place were those which had been found to be non-separable by chemical pro- cesses from one another, and from the element already occupying that place, if it was occupied, before the discovery of radio-actvity. For this reason the term isotope was coined to express an element chemically non-separable from the other, the term signifying the same place.
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The Complexity of the Chemical Elements 2 . Nature 99, 433–438 (1917). https://doi.org/10.1038/099433c0
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DOI: https://doi.org/10.1038/099433c0