# How is each element unique on the periodic table?

By their $\text{atomic numbers Z}$.
Each element is defined by a particular $\text{atomic number Z}$, where $Z$ is the number of protons, massive, positively charged particles in the element's nucleus.
$Z = 1$, $\text{the element is hydrogen}$; $Z = 2$, $\text{the element is helium}$; $Z = 3$, $\text{the element is lithium}$;........................................................$Z = 23$, $\text{the element is vanadium}$.