mass number

American  

noun

Physics.

1. 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. A

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mass number British  

noun

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

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mass number Scientific  

1. 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.

2. Also called nucleon number

3. Compare atomic mass atomic weight

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Etymology

Origin of mass number

First recorded in 1920–25

Compare meaning

How does mass-number compare to similar and commonly confused words? Explore the most common comparisons:

• mass number vs. atomic mass
• atomic number vs. mass number
• atomic weight vs. mass number

Example Sentences

See Examples For:

mass number

As an example, the masses and radii of all nuclei up to mass number 50 were calculated using this method.

From Science Daily ● May 15, 2024

Electron capture has the same effect on the nucleus as does positron emission: The atomic number is decreased by one and the mass number does not change.

From Textbooks ● Feb. 14, 2019

There is no change in mass number or atomic number during the emission of a γ ray unless the γ emission accompanies one of the other modes of decay.

From Textbooks ● Feb. 14, 2019

If the atomic number and the mass number of all but one of the particles in a nuclear reaction are known, we can identify the particle by balancing the reaction.

From Textbooks ● Feb. 14, 2019

The nation is an army which can bring to bear mass, number, and force, but not an assembly of free men in which each individual depends for his value on himself.

From Amiel's Journal by Ward, Humphry, Mrs.