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Standard and conventional atomic weights 2016 abridged to four significant digits

November 9, 2016

To indicate that atomic weights of many elements are not constants of nature, in 2009 and 2011 the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) replaced single-value standard atomic weight values with atomic weight intervals for 12 elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium). CIAAW recognized that some users of atomic weight data only need representative values for these 12 elements, such as for trade and commerce. For this purpose, CIAAW provides conventional atomic weight values, and these values can serve in education when a single representative value is needed, such as for molecular weight calculations. Because values abridged to four figures are preferred by many educational users of atomic weights, conventional atomic weight values abridged to four figures for all 12 elements (except for lithium, which is three figures) have been determined and are presented in a table "Standard and conventional atomic weights 2016 abridged to four significant digits".