What three factors determine the reactivity of an element?

1: The number of valence electrons, all elements want eight, so if they have eight, non-reactive, if they have 1 or 7, highly reactive.

2: Type of element, non-metal or metal, noble gas, halogens and alkalis.

3: Lastly the actual overall number of electrons, because that totals to what it has in its shell and what does it do/have.