# How are the nuclei of magnesium and sodium different?

Mar 20, 2016

For a start, the atomic numbers each element are (necessarily) different.

#### Explanation:

For $N a$, $Z$, the atomic number $=$ $11$; there are thus 11 massive, positively charged particles in each $N a$ nucleus. For $M g$, there are $12$ such particles. Of course, the common isotopes of each metal have different number of neutrons, massive, neutrally charged particles in the nucleus.

What distinguishes one element from another, is always $Z$, the atomic number. A given selection of nuclei of the same element, NECESSARILY have, the same $Z$, but they might have different number of neutrons. The protium nucleus, ""^1H, is mightily common, but there are hydrogen nuclei with a neutron in the nucleus, to give the deuterium isotope, ""^2H. ""^1H and ""^2H, and even $\text{^3H" (tritium)}$, for instance, are isotopes of elemental hydrogen.