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Inorganic Chemistry Division (II)


Number: 1999-043-1-200 [ 990431/200/00 ]

Title: Element by Element Review of Atomic Weights to the Year 2000

Task Group
J.R. de Laeter

Members: J.K. Bohlke, P. De Bièvre, H. Hidaka, H.S. Peiser, K.J.R. Rosman, P. Taylor

Completion Date: 2002 - project completed

A Review article of the science of atomic weights.

The review describes the information on the isotopic compositions and atomic weights of the elements as evaluated regularly by the Commission on Atomic Weights and Isotopic Abundances.

The Review aims:

(i) to describe the developments in atomic weights determinations during the 20th Century.

(ii) to give current best values of the atomic weights and isotope abundances of each element with their associated uncertainties;

(iii) the literature sources of these values and

(iv) the known limitations to the applicability of these values.

A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to moral, legal and international standards. Relative atomic weights were originally determined by elemental mass measurements coupled with an understanding of chemical stoichiometry, but are now based almost entirely on a knowledge of the isotopic composition and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled so that the numeric values for the carbon isotope of mass 12 is 12 exactly, and these quantities are invariably associated with carefully defined, estimated uncertainties.

This review reflects the current and increasing interest of science in the measured differences between source-specific and even sample-specific atomic weights. These relative comparisons can often be made with a smaller uncertainty that is achieved in the best calibrated atomic-weight determinations. As well as unequivocally determining the origin of chemical compounds, accurate determinations of the atomic weights of certain elements also effect the values of a number of fundamental constants.

A subset of the writing group will be meeting in mid-June, in Belgium, to finalize the manuscript. Publication in PAC and annoncement in CI will follow.

Project completed - IUPAC Technical Report published in Pure Appl. Chem. 75(6), 683-799, 2003.

Last update: 10 June 2003


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