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News & Notices

Standard Atomic Weights Revised

The Commission on Isotopic Abundances and Atomic Weights (II.1) met for two days, on 10-11 August 2005, during the 43rd IUPAC General Assembly in Beijing. Following its meeting, the Commission released the changes to the standard atomic weights, Ar(E), of 16 chemical elements. The following changes are based on new determinations of isotopic abundances and reviews of previous isotopic abundances and atomic masses:

From To
Aluminium 26.981 538 (2) 26.981 5386 (8)
Bismuth 208.980 38 (2) 208.980 40 (1)
Caesium 132.905 45 (2) 132.905 4519 (2)
Cobalt 58.933 200 (9) 58.933 195 (5)
Gold 196.966 55 (2) 196.966 569 (4)
Lanthanum 138.9055 (2) 138.905 47 (7)
Manganese 54.938 049 (9) 54.938 045 (5)
Neodymium
144.24 (3)
144.242 (3)
Phosphorus 30.973 761 (2) 30.973 762 (2)
Platinum
195.078 (2)
195.084 (9)
Samarium
150.36 (3)
150.36 (2)
Scandium 44.955 910 (8) 44.955 912 (6)
Sodium 22.989 770 (2) 22.989 769 28 (2)
Tantalum
180.9479 (1)
180.947 88 (2)
Terbium 158.925 34 (2) 158.925 35 (2)
Thorium 232.0381 (1) 232.038 06 (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(Al) = 26.981 538 (2) is the concise form of the expression Ar(Al) = 26.981 538 ± 0.000 002

These changes in the atomic weights will be published in a new Table of Standard Atomic Weights 2005, which will be submitted for publication in Pure and Applied Chemistry* by the end of 2005. The commission also continued its review of publications of variations in the natural isotopic abundances. For more details about the Commission meeting in Beijing, see Chem. Int. Nov/Dec 2005 issue, Division Roundups on p. 7, or contact Michael E. Wieser <mwieser@ucalgary.ca>, secretary of the Commission.

first posted 19 Oct 05

* IUPAC Technical Report published as Pure Appl. Chem. 78(11), 2051-2066, 2006

 

<release published in Chem. Int. Nov/Dec 2005 issue>

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