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Mass Number Definition

Definition of Mass Number

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Mass number is the sum of the number of protons and neutrons in an atom.

Mass number is the sum of the number of protons and neutrons in an atom.

Todd Helmenstine
Mass Number Definition: An integer equal to the sum of the number of protons and neutrons of an atomic nucleus.

Examples: 3717Cl has a mass number of 37. Its nucleus contains 17 protons and 20 neutrons.

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