News & Notices

Standard Atomic Weights Revised

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, A_r(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:

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, A_r(Zn) = 65.38(2) is the concise form of the expression A_r(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