Item

Abstract

The IUPAC Commission on Isotopic Abundances and Atomic
Weights has changed the way certain atomic weights are
reported [1–3]. In particular, the fixed ‘standard atomic weight’
has been replaced by an atomic weight ‘interval’ for ten predominantly
light elements (H, Li, B, C, N, O, Si, S, Cl and Tl),
reflecting the variability of their isotopic composition. Although
the respective span (the ‘range’) may not be large, the precise
atomic weight of an element in a particular batch or reservoir has
to be estimated from other material properties, or has to measured
with higher precision, depending on experimental requirements.
In the future, the atomic weight intervals are expected to
increase with new findings, such as the discovery of new materials or isotopically exotic sources of materials, rather than becoming more tightly constrained by new measurements.