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 slightly: 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 today.

CIAAW chair Johanna Irrgeher says in an email that “these three elements were chosen for revision because new data of outstanding scientific quality had been published,” including several studies from the National Research Council Canada. “The commission requires detailed studies to assess the validity of new values, and only considers data that meet the highest standards of transparency, traceability, and analytical precision.”

These three elements are considered critical to technology. MRI contrast agents made with gadolinium help doctors to visualize blood vessels, tumors, and areas of inflammation. IUPAC last revised its atomic weight in 1969 using isotopic abundance measurements made in the 1940s.

Zirconium has applications in the nuclear and aerospace industries; it is also used biomedically in dental implants and joint replacements. IUPAC last revised zirconium’s atomic weight in 1983.

Lutetium has fewer applications but can be used as a chemical catalyst or in radionuclide therapy. Its atomic weight was last revised relatively recently—2007.