The number of protons - St. Paul's Intermediate School

Nickel has a lower atomic mass than cobalt, even though it has a higher atomic number. One possible explanation is that one of the average atomic masses was miscalculated. In the case of cobalt, there is only one isotope: 100% 59Co at a mass of 58.9332 amu. For nickel, however, there are five isotopes as given in the table. ... ................
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