Really Simple GCSE question about G1 and G7

I've never quite understood this...how come reactivity increases as you go down group 1, but decreases down group 7?

I know with group 1, reactivity increases because the outer electron is further from the nucleus each time so the forces of attraction are weaker (thus the electron is more easy to lose), but I don't get why the same doesn't apply to group 7? Why do those elements have less inclination to gain a full outer shell?

Can anyone help me in simple GCSE terms?

Reply 1

dezlee

Group 7 elements would want to gain a full outer shell, but would they do it in the same way, as in lose them all?

Elements in Group 7 don't want to lose 7 electrons. they would want to gain an extra electron...

it's easier.
Thus, to gain an electron, they would want a larger nuclear force, which is where there are less electron shells for shielding.

Therefore, reactivity is higher when ther are less electron shells, ie. fluorine.