# What are the subatomic particles contained in the nucleus of an atom?

Protons are massive, positively charged nuclear particles. The number of protons gives $Z$, the atomic number, which defines the identity of the element. Neutrons are massive, neutrally charged nuclear particles. A given element can support different numbers of neutrons, and thus the phenomenon of isotopes arises.
In a neutral atom of given $Z$, what is the number of electrons?