Pure and Applied Chemistry

The biennial review of atomic-weight, A_r(E), determinations and other cognate data have resulted in changes for the standard atomic weights of the following elements:

element	From	To
nitrogen	14.006 74 ± 0.000 07	14.0067 ± 0.0002
sulfur	32.066 ± 0.006	32.065 ± 0.005
chlorine	35.4527 ± 0.0009	35.453 ± 0.002
germanium	72.61 ± 0.02	72.64 ± 0.01
xenon	131.29 ± 0.02	131.293 ± 0.006
erbium	167.26 ± 0.03	167.259 ± 0.003
uranium	238.0289 ± 0.0001	238.028 91 ± 0.000 03

Presented are updated tables of the standard atomic weights and their uncertainties estimated by combining experimental uncertainties and terrestrial variabilities. In addition, this report again contains an updated table of relative atomic-mass values and half-lives of selected radioisotopes. Changes in the evaluated isotopic abundance values from those published in 1997 are so minor that an updated list will not be published for the year 1999.

Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on parent nuclides that might affect isotopic abundances or atomic-weight values are included in this report for the information of the interested scientific community.