mass number

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noun Physics.

the integer nearest in value to the atomic weight of an atom and equal to the number of nucleons in the nucleus of the atom. Symbol: A

Origin of mass number

First recorded in 1920–25

Words nearby mass number

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British Dictionary definitions for mass number

mass number

noun

the total number of neutrons and protons in the nucleus of a particular atom Symbol: A Also called: nucleon number

Scientific definitions for mass number

mass number

The total number of protons and neutrons in the nucleus of an atom. For example, nitrogen has 7 protons and 7 neutrons in its nucleus, giving it a mass number of 14. Isotopes of elements are distinguished by their mass number; for example, carbon-12 and carbon-14 have mass numbers of 12 and 14 respectively. Also called nucleon number Compare atomic mass atomic weight.