Definition of mass number in English:

Share this entry

mass number

Pronunciation: /ˈmas ˌnəmbər/


The total number of protons and neutrons in a nucleus.
Example sentences
  • The sum of the protons and neutrons is called the mass number.
  • Various numbers are used to define nuclei: the atomic number, Z, is the number of protons, while the mass number is the sum of the atomic number and the number of neutrons, N.
  • The mass number gives you the total number of protons and neutrons in the nucleus of that element.

For editors and proofreaders

Syllabification: mass num·ber

Share this entry

What do you find interesting about this word or phrase?

Comments that don't adhere to our Community Guidelines may be moderated or removed.