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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    112Sn 111.904 825(2)0.0097(1)
    114Sn 113.902 7801(2)0.0066(1)
    115Sn 114.903 3447(1)0.0034(1)
    116Sn 115.901 7428(6)0.1454(9)
    117Sn 116.902 954(3)0.0768(7)
    118Sn 117.901 607(3)0.2422(9)
    119Sn 118.903 311(5)0.0859(4)
    120Sn 119.902 202(6)0.3258(9)
    122Sn 121.903 44(2)0.0463(3)
    124Sn 123.905 277(7)0.0579(5)

    In its 1961 report, the Commission recommended Ar(Sn) = 118.69 based on chemical-ratio determinations. From these measurements, with current values of the atomic weights of the other elements involved, the following atomic weights for Sn are derived: Ar(Sn) = 118.686, 118.691, and 118.701. The Commission was also aware that three mass-spectrometric determinations had been made that yield slightly higher atomic-weight values.

    Tin has ten stable isotopes, the largest number of all elements. Because of this, the isotopic composition measurements involve an unusually large number of experimentally determined ratios, each subject to uncertainty. In 1969, the Commission assessed Ar(Sn) = 118.69(3) therefore preferring the chemically determined atomic-weight values. This viewpoint was reaffirmed until 1983 when the Commission was able to consider the first calibrated mass-spectrometric measurement, which reported Ar(Sn) = 118.7099(22) and demonstrated good agreement with many previous isotope-abundance measurements (after correcting those uncalibrated measurements for isotope fractionation). In 1983 the Commission changed the basis for the standard atomic weight of tin to mass spectrometry and the value to Ar(Sn) = 118.710(7).

    The "g" annotation arises from the presence of naturally occurring fission products found in fossil reactors at Gabon, southwest Africa.

    SOURCE  Atomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
    © IUPAC 2003


    Ar(Sn) = 118.710(7) since 1983

    The name derives from the Anglo-Saxon tin of unknown origin. The symbol Sn is derived from Latin stannum for alloys containing lead. The element was known in prehistoric times.