# The number of protons in an atom equals the number of what?

Protons are conceived to be positively charged, massive nuclear particles. Electrons are conceived to be particles of negligible mass that orbit the nuclear core. Clearly, for a neutral atom, the number of electrons must equal the number of nuclear protons. The number of nuclear protons, $Z$, the atomic number, defines the identity of the nucleus: $Z = 1 , \text{ H";Z=2," He";Z=3," Li";Z=46," Pd} .$