What is the Mass Number (A)?

Written by J.A Dobado | Last Updated on April 22, 2024

The Mass Number corresponds to the total number of protons (p+) plus neutrons (n) that an atom has in its nucleus.

With the following equation, it is also possible to obtain the number of neutrons (n) of an atom.

To represent the atomic number (Z) and the mass number (A) of a chemical element, it is written down:

For example, the mass number of Fluorine is 19 and its atomic number is 9 (indicating that it has 9 protons in the nucleus). Thus. the number of neutrons in a fluorine atom is 19 – 9 = 10. Note that the atomic number, the number of neutrons and the mass number must be positive integers.+

Video about the Difference between Mass Number and Atomic Mass