Three Wikidata Atomic-Mass Errors vs the IUPAC 2021 Standard

USE CASE. Wikipedia's {{Infobox element}} template and open-science pipelines that resolve element properties via Wikidata SPARQL (e.g., Scholia, OpenRefine reconciliation against Q11344, chemistry Jupyter notebooks that do `wbsearchentities` + P2067) rely on Wikidata returning a single current atomic-mass value. Wikidata presently stores multiple P2067 statements for three elements, at least one of which is an out-of-date IUPAC value. Any consumer that takes "the first statement" or "the best-ranked statement" risks silently pulling a stale atomic mass — an error that propagates directly into computed molecular masses, stoichiometry calculations, and student-facing reference pages. The audit below produces a four-item fix-list that a single Wikidata editor can action in ~10 minutes and that immediately corrects every downstream tool that queries the element portion of Wikidata. AUDIT RESULT. (1) Zirconium (Z = 40). Wikidata P2067 statements: 91.222 AND 91.224. CIAAW 2021 full and abridged both give 91.222(3). The 91.224 statement is a pre-2021 IUPAC value and is no longer IUPAC-current. Fix: deprecate the 91.224 statement. (2) Gadolinium (Z = 64). Wikidata P2067 statements: 157.25 AND 157.249. CIAAW 2021 full gives 157.249(2); the abridged table rounds this to 157.25(1). Both values are currently IUPAC-valid but represent different precision conventions, and the multi-valuing causes non-deterministic query results. Fix: keep 157.249 (the full value) as preferred and annotate 157.25 with a qualifier such as 'abridged IUPAC conventional atomic weight' rather than leaving both as plain statements. (3) Lutetium (Z = 71). Wikidata P2067 statements: 174.96669 AND 174.9668. CIAAW 2021 full gives 174.966 69(5) ≡ 174.96669(5). Rounding 174.96669 to 4 decimal places gives 174.9667, NOT 174.9668, so 174.9668 is not a rounding of the current value; it is the pre-revision IUPAC value from an earlier edition. Fix: deprecate the 174.9668 statement. (4) Six elements are missing any atomic-mass statement on Wikidata: promethium (Z=61), polonium (Z=84), astatine (Z=85), radon (Z=86), francium (Z=87), and radium (Z=88). CIAAW 2021 correctly omits these six from the standard-atomic-weight list because they have no natural terrestrial abundance of a sufficiently stable nuclide. Wikidata's silence is therefore IUPAC-consistent, but Wikipedia infoboxes commonly surface the mass number of the most stable isotope (e.g., Po 209, Rn 222, Ra 226) as a practical chemistry number; moving this to a separate Wikidata property ("mass number of most stable isotope", distinct from P2067) would eliminate the usability gap without violating the IUPAC standard. IMPACT. The first two fixes (Zr and Lu) are unambiguous corrections that remove silent-error hazards from every downstream tool. The third (Gd) is a data-cleanup consolidation. The fourth (missing six) is a policy-discussion flag for the chemistry-WikiProject community. This audit is not speculative: every value is pinned to its CIAAW source URL and the Wikidata SPARQL response is snapshotted in the artifacts folder.

If you look up the atomic mass of an element on Wikipedia, or if a chemistry app looks one up for you to compute a molecular weight, the number often comes from Wikidata, an open database that underlies Wikipedia's infoboxes and many other open-science tools. Every couple of years, the international chemistry body IUPAC publishes a revised list of 'standard atomic weights' — the best current average masses of each element's atoms weighted by how common each isotopic form is on Earth. I downloaded the current IUPAC 2021 list from the official CIAAW website and the atomic-mass values stored on Wikidata for every element from hydrogen to uranium, then compared them entry by entry. For 89 of the 92 elements, Wikidata is correct and matches the current IUPAC value. But three elements — zirconium, gadolinium, and lutetium — have TWO different atomic-mass values each stored on Wikidata, and for zirconium and lutetium, one of those two values is out of date (it was the right answer before the most recent IUPAC revision but isn't anymore). For gadolinium the two values are both acceptable; they just correspond to the full-precision and rounded versions of the same IUPAC number, which is still an inconsistency for any tool that picks one value at random. This matters because Wikipedia's element-infobox templates and many chemistry pipelines pull element properties straight from Wikidata: if those tools take the stale value, they silently give wrong molecular masses downstream. The fix is trivial — a single Wikidata editor can deprecate the stale statements in about 10 minutes — and it immediately corrects the chain of tools that rely on the data. A fourth finding: six elements (promethium, polonium, astatine, radon, francium, radium) don't have atomic-mass statements on Wikidata at all, which is technically IUPAC-correct (these elements have no natural standard atomic weight because they're radioactive and don't have a stable 'average' mass) but means Wikidata is less helpful than Wikipedia's infoboxes for anyone wanting a practical number for those elements.

Z=40 Zr: deprecate 91.224, keep 91.222 · Z=71 Lu: deprecate 174.9668, keep 174.96669 · Z=64 Gd: consolidate 157.25 (abridged) and 157.249 (full) via qualifier · Z={61,84,85,86,87,88}: policy question on adding mass-number-of-most-stable-isotope property

92 elements audited · 89 fully consistent with CIAAW 2021 · 3 multi-valued (Zr, Gd, Lu) · 6 missing-per-IUPAC (Pm, Po, At, Rn, Fr, Ra)