# On the Periodic Table of elements, there are atomic numbers for each element. What is their relevence? How do you calculate them?

The atomic number. $Z$, is the number of protons, positively charged, massive nuclear particles. It defines the identity of the element.
$Z = 1$, the element is $H$, $Z = 2$, the element is $H e$, $Z = 3$, the element is $L i$, $Z = 4$, the element is $B e$,..................$Z = 26$, the element is $F e$, etc..........