Commission on
Atomic Weights and Isotopic Abundances (II.1)
Summary of Minutes
of Commission Meeting at IUPAC General Assembly, Berlin, Germany, 8-10
August 1999
The Commission on Atomic Weights and Isotopic Abundances
(II.1) met for three days of discussions under the chairmanship of Prof.
Ludolf Schultz during the 40th IUPAC General Assembly in Berlin. The
standard atomic weights of seven chemical elements have been changed
significantly. Based on new determinations of isotopic abundances and
reviews of previous isotopic abundances, the standard atomic weight
of nitrogen was changed from 14.00674(7) to 14.0067(2), of sulfur from
32.066(6) to 32.065(5), of chlorine from 35.4527(9) to 35.453(2), of
germanium from 72.61(2) to 72.64(1), of xenon from 131.29(2) to 131.293(6),
of erbium from 167.26(3) to 167.259(3), and of uranium from 238.0289(1)
to 238.02891(3). Many of these changes were adopted so that standard
atomic-weight values more accurately reflect the values of these chemical
elements in naturally occurring materials.
The changes in atomic-weight values will be reflected
in the Table of Standard Atomic Weights 1999, which will be submitted
for publication in Pure and Applied Chemistry (PAC) before the
end of the year. Also planned for publication in PAC is a report
on fourteen elements that show significant isotopic abundance variation
in naturally occurring materials. This report demonstrates that the
atomic weight of such elements can be significantly larger than the
uncertainties of measurement. Publication of an element-by-element review
was discussed and is planned for submission to PAC in 2000. The
Commission discussed a glossary of definitions specific to atomic-weight
and isotopic-abundance work in order that definitions generated would
be submitted to nomenclature commissions for inclusion in future IUPAC
documents. A large number of isotopic-abundance measurements in extraterrestrial
materials is available; these data will be summarized and a draft will
be available at the next General Assembly in Brisbane in 2001.
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Tyler B. Coplen II
Chairman, IUPAC Commission II.1,
Subcommittee on Natural Isotopic Fractionation