||I U P A C
Organizations & People
Pure Appl. Chem.,
Vol. 70, No. 1, pp. 237-257, 1998.
COMMISSION ON ATOMIC WEIGHTS AND
History of the Recommended
Atomic-Weight Values from 1882 to 1997: A Comparison of Differences
from Current Values to the Estimated Uncertainties of Earlier Values
B.Coplen and H. S.
World Wide Web version
International commissions and national
committees for atomic weights (mean relative atomic masses) have recommended
regularly updated, best values for these atomic weights as applicable
to terrestrial sources of the chemical elements. Presented here is a
historically complete listing starting with the values in F. W. Clarke's
1882 recalculation, followed by the recommended values in the annual
reports of the American Chemical Society's Atomic Weights Commission.
From 1903, an International Commission published such reports and its
values (scaled to an atomic weight of 16 for oxygen) are here used in
preference to those of national committees of Britain, Germany, Spain,
Switzerland, and the U.S.A. We have, however, made scaling adjustments
from Ar(16O) to Ar(12C)
where not negligible. From 1920, this International Commission constituted
itself under the International Union of Pure and Applied Chemistry (IUPAC).
Since then, IUPAC has published reports (mostly biennially) listing
the recommended atomic weights, which are reproduced here. Since 1979,
these values have been called the "standard atomic weights"
and, since 1969, all values have been published with their estimated
uncertainties. Few of the earlier values were published with uncertainties.
Nevertheless, we assessed such uncertainties on the basis of our understanding
of the likely contemporary judgement of the values' reliability. While
neglecting remaining uncertainties of 1997 values, we derive "differences"
and a retrospective index of reliability of atomic-weight values in
relation to assessments of uncertainties at the time of their publication.
A striking improvement in reliability appears to have been achieved
since the commissions have imposed upon themselves the rule of recording
estimated uncertainties from all recognized sources of error.
View elements by periodic
View list of elements
Comment - Conclusion
- Acknowledgements - References
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