I  U  P  A  C

News & Notices

Organizations & People

Standing Committees







Links of Interest

Search the Site

Home Page



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, 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>

> link to FAQs - The Chemical Elements

Page last modified 28 November 2007.
Copyright © 2007 International Union of Pure and Applied Chemistry.
Questions or comments about IUPAC, please contact, the Secretariat.
Questions regarding the website, please contact web manager.