The IUPAC Commission on Isotopic Abundances and Atomic Weights (IUPAC CIAAW) regularly reviews literature data, leading to the identification of advancements in measurement science which leads to formal revisions of the recommended atomic weights of the elements (known as the standard atomic weight). This occurs rather infrequently, each element being affected, on average, once every two decades.
The CIAAW met in August 2023 in the Hague, the Netherlands, under the leadership of Prof. Johanna Irrgeher (Montanuniversität Leoben, Austria). Following this meeting, the CIAAW recommends changes to the standard atomic weights of gadolinium (Gd), lutetium (Lu), and zirconium (Zr) based on recent determinations and evaluations of their terrestrial isotopic abundances:
gadolinium: to 157.249 ± 0.002 from 157.25 ± 0.03
lutetium: to 174.966 69 ± 0.000 05 from 174.9668 ± 0.0001
zirconium: to 91.222 ± 0.003 from 91.224 ± 0.002
The CIAAW notes that the standard atomic weight of gadolinium was last revised in 1969 based on isotopic abundance measurements made in the 1940s. Since then, several studies dedicated to the measurement of the isotopic composition of gadolinium have been published which warrant a revised standard atomic weight. For lutetium and zirconium, there are more recent measurements available and their standard atomic weights were last revised by IUPAC in 2007 and 1983, respectively. These changes and considerations will be published in Pure and Applied Chemistry and can be found online at the website of the IUPAC Commission on Isotopic Abundances and Atomic Weights (ciaaw.org).
The importance of determining precise atomic weights has long been recognized, resulting in the creation of the International Atomic Weights Committee in 1899, now known as the IUPAC Commission on Isotopic Abundances and Atomic Weights.
IUPAC (www.iupac.org) was formed in 1919 by chemists from industry and academia, who recognized the need for international standardization in chemistry. Its most visible activity to most chemists is the standardization of the names and symbols of chemical elements and also the standardization of their atomic weights which is essential to the well-being and continued success of the scientific enterprise and to the smooth development and growth of international trade and commerce.
Technical contact:
Johanna Irrgeher, Chair CIAAW <johanna.irrgeher@unileoben.ac.at>
Media contact:
Fabienne Meyers, Associate Director IUPAC <fmeyers@iupac.org>
Image: (above) Periodic Table tiles for zirconium, gadolinium, and lutetium from ciaaw.org ; (featured) gadolinium from the IUPAC Periodic Table of the Elements and Isotopes at isotopesmatter.ca.
Release published in Chem Int, Jan 2025, p 20