The Commission on Isotopic Abundances and Atomic Weights (II.1) met in Pisa, Italy, prior the 44th IUPAC General Assembly held in Torino, Italy, 4-12 August 2007. Following its meeting, the Commission recommended significant changes to the standard atomic weights, Ar(E), of 5 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, which will be submitted for publication in Pure and Applied Chemistry by the end of 2007.
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.
first posted 23 August 07
<release published in Chem. Int. Nov 2007>
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