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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    64Zn 63.929 142(5)0.4917(75)
    66Zn 65.926 034(5)0.2773(98)
    67Zn 66.927 127(5)0.0404(16)
    68Zn 67.924 844(5)0.1845(63)
    70Zn 69.925 32(2) 0.0061(10)

    In 1961, the Commission recommended Ar(Zn) = 65.37 based on the chemical determinations. Meanwhile, mass-spectrometric determinations yielded a higher value of Ar(Zn) = 65.387.

    In 1971, coulometric determinations yielded Ar(Zn) = 65.377(3), whereupon the Commission changed the recommended value to 65.38(1). Soon, another mass-spectrometric value was published which yielded Ar(Zn) = 65.396(5). Faced with this ongoing discrepancy between chemical and physical values, in 1983 the Commission recommended Ar(Zn) = 65.39(2), explaining that the value was now weighted toward the mass-spectrometric measurement, but the uncertainty included the coulometric measurement. In 2001, Ar(Zn) was changed to 65.409(4) and in 2007 the Commission acknowledged that data influencing the 2001 decision could no longer be supported and recommended the current value of Ar(Zn) = 65.38(2). This change was unique in the sense that for the first time in the history of the Commission, the standard atomic weight (with its uncertainty) was outside the bounds of the previous value.


    Ar(Zn) = 65.38(2) since 2007

    The name derives from the German zink of unknown origin. It was first used in prehistoric times, where its compounds were used for healing wounds and sore eyes and for making brass. Zinc was recognized as a metal as early as 1374.

    Isotopic reference materials of zinc.