Radioactive Chemical Elements in the Atomic Weights Table

摘要

In the 1949 Report of the Atomic Weights Commission, a series of new elements were added to the Atomic Weights Table. Since these elements had been produced in the laboratory and were not discovered in nature, the atomic weight value of these artificial products would depend upon the production method. Since atomic weight is a property of an element as it occurs in nature, it would be incorrect to assign an atomic weight value to that element. As a result of that discussion, the Commission decided to provide only the mass number of the most stable (longest-lived) known isotope as the number to be associated with these entries in the Atomic Weights Table. As a function of time, the mass number associated with various elements has changed as longer-lived isotopes of a particular elements has been found in nature, or as improved half-life values of an element's isotopes might cause a shift in the longest-lived isotope from one mass number to another. In the 1957 Report of the Atomic Weights Commission, it was decided to discontinue the listing of the mass number in the Atomic Weights Table on the grounds that the kind of information supplied by the mass number is inconsistent with the primary purpose of the Table, i.e., to provide accurate values of 'these constants' for use in chemical calculations.