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Atomic weight
He · helium
헬륨
Takeaway
- Recommended or revised 8 times between 1902 and 2024 (first record 1902, latest revision 1983).
- The one revision whose previous recommendation had an uncertainty kept the new value inside the previous (expanded) range.
- The current standard atomic weight is 4.002 602(2) (recommended in 1983).
| 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 | 4.0 | no uncertainty | O=16 | 3.99985 | 10.1007/BF01370337 | |
| 1911 | 3.99 | no uncertainty | O=16 | 3.98985038 | 10.1021/ja01928a001 | |
| 1916 | 4.00 | no uncertainty | O=16 | 3.99985 | 10.1021/ja02176a001 | |
| 1931 | 4.002 | no uncertainty | O=16 | 4.00184992 | 10.1039/JR9310001617 | |
| 1938 | 4.003 | no uncertainty | O=16 | 4.00284989 | 10.1039/JR9380001101 | |
| 1961 | 4.0026 | no uncertainty | 12C=12 | 4.0026 | 10.1021/ja00881a001 | |
| 1969 | 4.002 60(1) | value(uncertainty) | 12C=12 | 4.0026 | 10.1351/pac197021010091 | |
| 1983 | 4.002 602(2) | value(uncertainty) | 12C=12 | 4.002602 | 0.200 | 10.1351/pac198456060653 |
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