What determines of something is reactive or nonreactive?

Answer 1

Reactions occur with Valence electrons. These are the outermost layer of electrons. In chemistry, there is a rule called the Octet rule, which says that atoms what to be as stable as possible and will do whatever they can do achieve that goal. For example, Sodium wants to lose 1 electron so that it can have a full outer shell of electrons (8). Thus, Sodium will very easily lose an electron to another element and is very reactive. Also, as you move down the Periodic Table and to the left, elements tend to be more reactive.