Definition: 'Mass Number'
mass numberType: Term
1. the mass of the atom of a particular isotope relative to hydrogen-1 (or to 1/12 the mass of carbon 12); generally very close to the whole number represented by the sum of the protons and neutrons in the atomic nucleus of the isotope (indicated in the name or symbol of the isotope, oxygen-16,
The information shown above for mass number is provided by Stedman's.
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