How do we find the number of neutrons in a nuclide, given Z, and the isotopic mass?

1 Answer
anor277
Jun 29, 2017

The number of neutrons equals the isotopic mass LESS the atomic number, Z.

Explanation:

To a first approximation, the mass of the nuclide is the number of massive nuclear particles, i.e. the number of protons (which number defines the atomic number, Z) and the number of neutrons, which number defines the isotope.

By way of example, the most abundant element in the universe is hydrogen, Z=1. All hydrogen nuclei have the one PROTON present in their nuclei. A small percentage of hydrogen nuclei contain ONE neutron, a massive, neutrally charged particle, to give the deuterium isotope, 2H; a smaller percentage of hydrogen nuclei contain TWO neutrons, a massive, to give the tritium isotope, 3H.

Most higher elements contain a number of isotopes, and their reported atomic mass is the weighted average of the individual isotopes.

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