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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    92Mo 91.906 808(5)0.146 49(106)
    94Mo 93.905 085(3)0.091 87(33)
    95Mo 94.905 839(3)0.158 73(30)
    96Mo 95.904 676(3)0.166 73(8)
    97Mo 96.906 018(3)0.095 82(15)
    98Mo 97.905 405(3)0.242 92(80)
    100Mo 99.907 472(7)0.097 44(65)

    In its 1961 report, the Commission recommended Ar(Mo) = 95.94 based on the chemical ratio measurements. Recalculation of their measurements based on current values of Ar(Ag) and Ar(Cl) gives Ar(Mo) = 95.939. In its 1975 report, the Commission evaluated five manuscripts dealing with mass-spectrometric determinations of the isotopic composition of molybdenum. Although they were judged not to be of equal reliability, their results all fall in the range of Ar = 95.93 to 95.94 in close agreement with the chemical value. Standard atomic weight of molybdenum was changed to its current value in 2013 as a result of a re-evaluation of isotopic measurements. The annotation "g" refers to anomalous occurrences at the Oklo natural nuclear reactor in Gabon.

    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(Mo) = 95.95(1) since 2013

    The name derives from the Greek molybdos for "lead". The ancients used the term "lead" for any black mineral that leaves a mark on paper. Molybdenum was discovered by the Swedish pharmacist and chemist Carl Wilhelm Scheele in 1778. It was first isolated by the Swedish chemist Peter-Jacob Hjelm in 1781.

    Isotopic reference materials of molybdenum.