Question

Question #9f407

Answer 1

From the number of valence electrons in their outermost shells.

Explanation:

All elements want to exist in nature as stable molecules. In order to do that, their electron configuration must follow the octet rule (eight electrons in the outermost shell).

Why? Because in nature, the only elements stable enough to exist on their own are noble gases with their electron configuration at `s^2` `p^6`. The eight electrons makes the element relatively unreactive in chemical reactions (except under certain conditions), which is why the other elements tend to either share, give or take electrons all for the sake of being stable molecules.