Question

What causes an element from the periodic table to be more or less reactive?

Answer 1

 an element from the periodic table to be more or less reactive is that they have a stable number of electrons and do not need to react with other atoms. All other atoms have less stable electron numbers,  they react with each other and share electrons to be more stable. The most reactive elements tend to have one or two electrons less or have one or two extra. 

Answer 2

All other atoms have less stable electron numbers, so they react with each other and share electrons to be more stable. The most reactive elements tend to be short one or two electron or have one or two extra.