Atomic Weights of Ten Chemical Elements About to Change

Source: USGS

A new Table of Standard Atomic Weights is published in Pure and Applied Chemistry. A companion article titled “Atomic Weights—No Longer Constants of Nature” is published in Chemistry International.

For the first time in history, a change will be made to the atomic weights of some elements listed on the Table of Standard Atomic Weights of the chemical elements found in the inside covers of chemistry textbooks worldwide.

The International Union of Pure and Applied Chemistry’s (IUPAC) Commission on Isotopic Abundances and Atomic Weights is publishing a new table that will express atomic weights of ten elements as intervals, rather than as single standard values. The new table is the result of cooperative research supported by the U.S. Geological Survey, IUPAC, and other contributing Commission members and institutions.

Standard atomic weights commonly are thought of as constants of nature, despite the fact that atomic weights of many common chemical elements show variations as a result of physical, chemical and biological processes.

“For more than a century and a half, many were taught to use standard atomic weights — a single value — found on the inside cover of chemistry textbooks and on the periodic table of the elements,” said Ty Coplen, director of the USGS Reston Stable Isotope Laboratory. “Though this change offers significant benefits in the understanding of chemistry, one can imagine the challenge now to educators and students who will have to select a single value out of an interval when doing chemistry calculations.”

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