Historical Atomic Weights

Summarized below are all standard atomic-weight values recommended by the CIAAW since its inaugural 1902 Atomic Weight Table.

Please enter the name or symbol of the element, or the year in order to retrieve the relevant historical standard atomic weights.

An entry is given only when the Commission recommended for the element a revised (or new) atomic-weight value. All values are given here as originally published by the Commission. Note that in 1961, the basis for expressing the atomic-weight values has been changed from m_a(O) = 16 to m_a(¹²C) = 12.
All names and symbols of the elements are given in their present form even though many changes have occured in this regard over the last century.

SOURCE (TEXT) Data compiled by Juris Meija from the CIAAW Atomic Weight reports spanning time period of 1902-2021.
© CIAAW 2016-2022 (last updated in March 2022)

WIKIPEDIA COMMONS

John Dalton (1766-1844) published the first atomic-weight table of the elements in the early 19th century.

A compilation and analysis of recommended atomic-weight values from 1882 to 1997 has been published by the Commission in 1998. History of the recommended atomic-weight values from 1882 to 1997: A comparison of differences from current values to the estimated uncertainties of earlier values by T.B. Coplen, and H.S. Peiser. Pure Appl. Chem. 70, 237-257 (1998)