The total number of protons and neutrons in a nucleus.
More example sentences
- The sum of the protons and neutrons is called the mass number.
- Various numbers are used to define nuclei: the atomic number, Z, is the number of protons, while the mass number is the sum of the atomic number and the number of neutrons, N.
- The mass number gives you the total number of protons and neutrons in the nucleus of that element.
Definition of mass number in:
- The British & World English dictionary