Other pages in this series (5)
A5
Switch to interval notation
Elements whose single value was replaced by an interval
Takeaway
- Since 2009, 14 elements, hydrogen and carbon among them, have been given as an interval rather than a single value, because their isotopic composition varies in nature.
- In all 14, the new interval contains the previous value; the median interval is 2.6 times as wide as the previous range.
- Definition
- Since 2009 CIAAW has written the standard atomic weight of elements with large natural variation in isotopic composition as an interval [lower, upper] instead of a value with an uncertainty. The value and uncertainty just before the switch are compared with the new interval.
- Formula
- Does the interval contain the previous value? Width ratio = (upper − lower) / (2 × previous uncertainty).
- Denominator
- 14 elements switched to an interval (2009–2020).
- How to read it
- In all 14, the new interval contains the previous value. The median interval is 2.6 times as wide as the previous range; argon widened most (85.5 times).
- Caveats
- An interval is not an uncertainty but the range of atomic weights actually found in normal materials, so intervals are not used as denominators in A2 and A3.
| Symbol | Previous | Interval | Width ratio | Contains previous |
|---|---|---|---|---|
| B | 1995: 10.811(7) | 2009: [10.806, 10.821] | 1.1 | yes |
| C | 1995: 12.0107(8) | 2009: [12.0096, 12.0116] | 1.2 | yes |
| Cl | 1999: 35.453(2) | 2009: [35.446, 35.457] | 2.8 | yes |
| H | 1981: 1.007 94(7) | 2009: [1.007 84, 1.008 11] | 1.9 | yes |
| Li | 1983: 6.941(2) | 2009: [6.938, 6.997] | 14.8 | yes |
| N | 1999: 14.0067(2) | 2009: [14.006 43, 14.007 28] | 2.1 | yes |
| O | 1969: 15.9994(3) | 2009: [15.999 03, 15.999 77] | 1.2 | yes |
| S | 1999: 32.065(5) | 2009: [32.059, 32.076] | 1.7 | yes |
| Si | 1975: 28.0855(3) | 2009: [28.084, 28.086] | 3.3 | yes |
| Tl | 1985: 204.3833(2) | 2009: [204.382, 204.385] | 7.5 | yes |
| Br | 1965: 79.904(1) | 2011: [79.901, 79.907] | 3.0 | yes |
| Mg | 1985: 24.3050(6) | 2011: [24.304, 24.307] | 2.5 | yes |
| Ar | 1979: 39.948(1) | 2017: [39.792, 39.963] | 85.5 | yes |
| Pb | 1969: 207.2(1) | 2020: [206.14, 207.94] | 9.0 | yes |
Download CSV: aw_a5_intervals.csv
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