Atomic Weight of Barium | Commission on Isotopic Abundances and Atomic Weights
| Isotope | Atomic mass (Da) | Isotopic abundance (amount fraction) |
|---|---|---|
| 130Ba | 129.906 32(2) | 0.0011(1) |
| 132Ba | 131.905 061(7) | 0.0010(1) |
| 134Ba | 133.904 508(2) | 0.0242(15) |
| 135Ba | 134.905 689(2) | 0.0659(10) |
| 136Ba | 135.904 576(2) | 0.0785(24) |
| 137Ba | 136.905 827(2) | 0.1123(23) |
| 138Ba | 137.905 247(2) | 0.7170(29) |
In 1961, the Commission recommended a value of Ar(Ba) = 137.34 based both on the chemical data and on mass-spectrometric abundance measurements. In 1975, the Commission reviewed the above data as well as new mass-spectrometric measurements. All of these measurements fell within a very narrow range, and recommended Ar(Ba) = 137.33(1). This value was revised in 1985 to 137.327(7) as a result of new guidelines for evaluating the uncertainty of atomic weights.
SOURCE Atomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800© IUPAC 2003
CIAAW
Barium
Ar(Ba) = 137.327(7) since 1985
The name is derived from the Greek barys for "heavy" because it was found in the mineral heavy spar (BaSO4). It was discovered by the Swedish pharmacist and chemist Carl Wilhelm Scheele in 1774 and first isolated by the British chemist and physicist Humphry Davy in 1808.