Weighty matters for 3 elements

Keepers of precise periodic tables, it’s time to make some changes. The International Union of Pure and Applied Chemistry Commission on Isotopic Abundances and Atomic Weights (IUPAC CIAAW) has issued revised atomic weights for zirconium, gadolinium, and lutetium. The revisions slim down all three elements: zirconium’s atomic weight changes to 91.222 ± 0.003 from 91.224 ± 0.002; gadolinium’s atomic weight changes to 157.249 ± 0.002 from 157.25 ± 0.03; and lutetium’s atomic weight changes to 174.96669 ± 0.00005 from 174.9668 ± 0.0001. Atomic weights are based on recent determinations and evaluations of elements’ terrestrial isotopic abundances. These can change as measurement science improves. Although revisions happen infrequently—IUPAC CIAAW estimates that each element is affected, on average, every 2 decades—the committee regularly reviews the data from the literature and met in August 2023 to discuss potential revisions, which were formally made Oct. 23, 2024 . CIAAW chair Johanna Irrgeher says in