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Atomic weight
H · hydrogen
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Takeaway
- Recommended or revised 10 times between 1902 and 2024 (first record 1902, latest revision 2009).
- Of 3 revisions whose previous recommendation had an uncertainty, 1 (1969) put the new value outside the previous (expanded) range.
- Since 2009, it has been given as the interval [1.007 84, 1.008 11] rather than a single value (the range found in normal materials).
| Yearyear of the recommendation | Value (as printed)as printed in CIAAW's table; digits in parentheses are the uncertainty (expanded range) in the last digits | Notationvalue(uncertainty), interval or no uncertainty | Scalebefore 1961 oxygen = 16, from 1961 ¹²C = 12 | Value, ¹²C scalepre-1961 values multiplied by 15.9994/16 | z vs previous(new − previous) ÷ previous uncertainty | ReportDOI of the CIAAW report |
|---|---|---|---|---|---|---|
| 1902 | 1.01 | no uncertainty | O=16 | 1.00996212 | 10.1007/BF01370337 | |
| 1903 | 1.008 | no uncertainty | O=16 | 1.0079622 | 10.1021/ja02003a001 | |
| 1931 | 1.0078 | no uncertainty | O=16 | 1.00776221 | 10.1039/JR9310001617 | |
| 1938 | 1.0081 | no uncertainty | O=16 | 1.0080622 | 10.1039/JR9380001101 | |
| 1940 | 1.0080 | no uncertainty | O=16 | 1.0079622 | 10.1039/JR9400000475 | |
| 1961 | 1.007 97(1) | value(uncertainty) | 12C=12 | 1.00797 | 10.1021/ja00881a001 | |
| 1969 | 1.0080(3) | value(uncertainty) | 12C=12 | 1.008 | 3.000 | 10.1351/pac197021010091 |
| 1971 | 1.0079(1) | value(uncertainty) | 12C=12 | 1.0079 | −0.333 | 10.1351/pac197230030637 |
| 1981 | 1.007 94(7) | value(uncertainty) | 12C=12 | 1.00794 | 0.400 | 10.1351/pac198355071101 |
| 2009 | [1.007 84, 1.008 11] | interval | 12C=12 | 1.007975 (interval midpoint, for calculation) | 10.1351/PAC-REP-10-09-14 |
Source: Standard atomic weights © IUPAC/CIAAW 2016–2024. Commission on Isotopic Abundances and Atomic Weights, Historical changes of standard atomic weights (compiled by J. Meija), https://www.ciaaw.org/historical-atomic-weights.htm