Mass Number

The mass number (A) of an atom is the number of protons and neutrons it has in its nucleus; e.g., A = 35 for a chlorine atom which contains 18 neutrons (35Cl), and A = 37 for one which contains 20 neutrons (37Cl).

In nuclide symbols the mass number is given as a leading superscript.

In isotope names (e. g. carbon-14, sodium-23) the mass number is the number following the element name.

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Beryllium 9 Clip
Carbon 12 Clip
Deuterium 2 Clip
Helium 4 Clip
Nitrogen 14 Clip
Oxygen 16 Clip
Tritium 3 Clip
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See also: Atomic Mass Unit, Atomic Number, Nuclide Symbol, Proton.

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Subjects: Physics