Following the reviews of atomic-weight determinations and other cognate data in 2015, 2017, 2019 and 2021, the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) has released the “Standard Atomic Weights of the Elements 2021” (Pure and Applied Chemistry, 4 May 2022; https://doi.org/10.1515/pac-2019-0603). As it is customary, the Report summarizes definitions of general terms and reviews the main reasons that limit our knowledge about the atomic weights of the elements: the nuclide masses (for F, P, Na, as an example), isotope ratio measurements (Zn, Yb, Mo), or variations of isotopic composition among natural materials (H, C, O). The Table of Standard Atomic Weights (TSAW) is at the center of this IUPAC Technical Report. The number of significant digits reported in the Standard Atomic Weights exceeds in many cases the needs of users and, in some cases, a single atomic-weight value is needed for further calculations. These are called abridged standard atomic weights.
IUPAC also provides an updated Periodic Table (released 4 May 2022) which contains these latest revisions listing the abridged atomic weights along with their +/− values. In this Periodic Table, and for all radioactive elements that lack isotopes with a characteristic isotopic abundance in natural terrestrial samples, the mass number of the nuclide with the longest confirmed half-life is listed between square brackets.
With this release of the TSAW, IUPAC celebrates the World Metrology Day 2022 (May 20), themed this year “Metrology in the Digital Era.” In recent years, CIAAW has made all its updates available online first, and has strived to serve researchers both in classical and digital research environment through its website ciaaw.org.
The Report “Standard Atomic Weights of the Elements 2021” is available ahead of print since 4 May 2022 and will soon appear in the IUPAC scientific journal Pure and Applied Chemistry. All updates for standard atomic weights can also be found on-line at the website of the IUPAC Commission on Isotopic Abundances and Atomic Weights (www.ciaaw.org).