How do atomic numbers change in the periodic table?

There are about 100 or so elements...and the elements are differentiated by the NUMBER of protons, massive, positively-charged particles, present in the element's nucleus. The actual number of nucular protons, gives #Z_"the atomic number"#. And I think this is simpler than chemists deserve.

#"Z=1, the element is hydrogen; Z=2, the element is helium;"# #"Z=3, the element is lithium;..... Z=92, the element is uranium.."#

You don't have to remember these numbers, because a Periodic Table should always be available. However, you do have to explain its significance. Also present in the nucleus of some atoms are NEUTRONS, massive, neutrally-charged particles, and these can vary from element to element and WITHIN the same element, and this gives to the phenomenon of isotopes.

For hydrogen, the most abundant element in the universe, most nuclei contain NO neutrons, to give the protium isotope, which we represent as #""^1H#, some hydrogen nuclei contain a proton AND a neutron to give #""^2H#, the deuterium isotope. And fewer still hydrogen nuclei contain TWO NEUTRONS, to give #""^3H#, the tritium isotope. Higher elements, express a larger isotopic distribution, and the atomic mass quoted on the Periodic Table is the weighted average of ALL the isotopes.

In the nuclear core of the element, the massive particles, the protons and neutrons, engage in the strong nuclear force, an attractive force, the which at short nuclear ranges is STRONGER than the electrostatic force of repulsion that operates betweens like-charged particles....

Got all that...?