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Vol. 29 No. 6
November-December 2007

IUPAC Wire | News and information on IUPAC, its fellows, and members organizations
See also www.iupac.org/news

Standard Atomic Weights Revised

The IUPAC Commission on Isotopic Abundances and Atomic Weights (II.1) met in Pisa, Italy, just prior to the 44th IUPAC General Assembly held 4–12 August 2007, in Torino, Italy. The commission meeting recommended significant changes to the standard atomic weights, Ar(E), of five chemical elements. The following changes are based on new determinations of isotopic abundances and reviews of previous isotopic abundances and atomic masses:

  From To
lutetium 174.967(1) 174.9668(1)
molybdenum 95.94(2) 95.96(2)
nickel 58.6934(2) 58.6934(4)
ytterbium 173.04(3) 173.054(5)
zinc 65.409(4) 65.38(2)
The values are presented in a concise notation whereby the standard uncertainty is given in parenthesis next to the least significant digits to which it applies; for example, Ar(Zn) = 65.38(2) is the concise form of the expression Ar(Zn) = 65.38 ± 0.02.

In addition, the recommended value for the isotope amount ratio of 40Ar/36Ar, which may be of importance to geochronologists, has been changed from 296.03(53) to 298.56(31).
These changes will be published in a new Table of Standard Atomic Weights 2007, to be submitted for publication in Pure and Applied Chemistry by the end of the year. For more details about the commission, see <www.iupac.org/divisions/II/II.1>, or contact Michael E. Wieser <mwieser@ucalgary.ca>, secretary of the commission.

www.iupac.org/news/archives/2007/atomic-weights_revised07.html


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