Question

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

Answer 1

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

Explanation:

Nuclei are conceived to contain `"protons"`, fundamental, massive charged particles, and `"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 `"protons"` determines the identity of the element. `Z=1`, `"hydrogen"`; `Z=2`, `"helium"`; `Z=3`, `"lithium"`;...........................`Z=45`, `"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, `""^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.