Standard Atomic Weight of Hafnium Revised

The IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) met under the chairmanship of Dr. Juris Meija (Canada), at the Federal Institute for Materials Research and Testing (, Berlin Germany, in June 2019. As IUPAC celebrates its centennial in 2019, its oldest body, the CIAAW, turns 120 with its beginnings tracing back to Berlin in 1899 [1]. Following its 2019 meeting, the CIAAW recommended changes to the standard atomic weight (i.e. relative atomic mass) of hafnium based on recent determinations and evaluations of its isotopic composition:

hafnium: to 178.486 ± 0.006 from 178.49 ± 0.02

The CIAAW continues to recognize the extent of natural variations in the atomic weights of the elements. For example, radioactive decay of lutetium alters the isotopic composition of hafnium by producing the light isotope of hafnium-176. Thus, some rare terrestrial materials can have abnormal isotopic compositions of hafnium with the most extreme known case being sedimentary chert from South Africa having atomic-weight value of 178.447.

The CIAAW continues to evaluate literature data which leads to identification of developments in the measurement science, recognition of new discoveries, and remains committed to modernize its technical guidelines and work towards further expansion of its website to include more historical databases.

These changes and considerations will be published in Pure and Applied Chemistry [2] and can be found online at the website of the IUPAC Commission on Isotopic Abundances and Atomic Weights (


On behalf of the CIAAW
Juris Meija, Chair CIAAW


[1] For a historical account of the CIAAW, see J.R. De Laeter and J. Meija (23 Jan 2019) “A Weighted Service to Chemistry” IUPAC 100 Stories. Retrieved from and references therein.

[2] The “Atomic Weights of the Elements 2017” is to appear next in Pure and Applied Chemistry; see for release.

Announcement published in Chem Int April 2020, p. 31

Comments are closed.