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    IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
    92Mo 91.906 807(1)0.146 49(106)
    94Mo 93.905 084(1)0.091 87(33)
    95Mo 94.905 8374(8)0.158 73(30)
    96Mo 95.904 6748(8)0.166 73(8)
    97Mo 96.906 017(1)0.095 82(15)
    98Mo 97.905 404(1)0.242 92(80)
    100Mo 99.907 468(2)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.