The nucleus — Define

Define proton number (atomic number) Z and nucleon number (mass number) A, and explain how to find the number of neutrons in a nucleus.

Proton number (atomic number), Z, is the number of protons in the nucleus of an atom. Nucleon number (mass number), A, is the total number of protons and neutrons (nucleons) in the nucleus. The number of neutrons in a nucleus is found using: number of neutrons = nucleon number - proton number (N = A - Z).