# How does the atomic number of an element identify it?

Jul 30, 2016

The atomic number, $Z$, reveals the number of protons, fundamental, massive, positively charged particles, present in the atomic nucleus.
If $Z = 1$, the element is hydrogen; if $Z = 2$, the element is helium; If $Z = 3$, the element is lithium;.........if If $Z = 26$, the element is iron; etc.
For hydrogen, $Z = 1$, and again since $Z = 1$, this is what identifies the atom as hydrogen. Most hydrogen nuclei contain only the 1 proton, the ""^1H or protium isotope. A small percentage of hydrogen atoms contain a neutron, and this we would represent as ""^2H, the deuterium isotope. A smaller percentage of hydrogen atoms contain 2 neutrons, to give ""^3H, the tritium isotope. I stress that protium, deuterium, and tritium are ALL isotopes of hydrogen because $Z = 1$; the presence of different numbers of neutrons in the nucleus gives rise to the isotopic distribution. Capisce?