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

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

Since an element’s isotopes will have slightly different mass numbers, scientists also determine the atomic mass, which is the calculated mean of the mass number for its naturally occurring isotopes.

From Textbooks • Jun. 9, 2022

The number of neutrons is therefore the difference between the mass number and the atomic number: A – Z = number of neutrons.

From Textbooks • Feb. 14, 2019

This continues up to A ≈ 60 , roughly corresponding to the mass number of iron.

From Textbooks • Aug. 12, 2015

In this system forces were considered inherent in matter, being expressed as mechanical movements, and determined by mass, number, and weight.

From A History of Science — Volume 4 by Williams, Henry Smith