# What is the number of protons and neutrons in the nucleus of an atom?

Dec 18, 2016

Well, their sum is the atomic mass of the nuclide.

#### Explanation:

Nuclei are conceived to contain $\text{protons}$, fundamental, massive charged particles, and $\text{neutrons}$, fundamental, massive particles of zero charge. On nuclear scales, the particles are so attracted by nuclear interactions that the electrostatic repulsion that operates between like charges is overcome.

The number of $\text{protons}$ determines the identity of the element. $Z = 1$, $\text{hydrogen}$; $Z = 2$, $\text{helium}$; $Z = 3$, $\text{lithium}$;...........................$Z = 45$, $\text{rhodium}$. Of course, you would know this well.

Individual elements can have various numbers of neutrons, and this variability gives rise to the existence of isotopes; the same element that has different number of neutrons. For instance, most hydrogen nuclei contain the one nuclide, the proton, to give the protium isotope, $\text{^1H}$; a few nuclei contain a proton and a neutron to give the deuterium isotope, ""^2H; and a smaller few nuclei contain a proton and 2 neutrons to give the tritium isotope, ""^3H,

As the nucleus gets bigger, a greater range of isotopes becomes possible, and the atomic masses quoted on the Periodic Table are the weighted average of the individual isotopes.