# How many neutrons and protons does a typical neutral atom of phosphorus have?

The ""^31P isotope is almost 100% abundant, $Z = 15$, and thus there are 16 neutrons.
The atomic number, $Z$, of phosphorus is $15$. That is there are 15 $\text{protons}$, fundamental, positively charged, massive particles in the phosphorus nucleus. This atomic number defines the elemental identitiy. If there are 15 protons, then to make up the isotopic mass, $31$, there must be 16 $\text{neutrons}$, 16 massive, neutrally charged particles in the element's nucleus.