I was wondering, as you go down a group, the atoms get bigger... This means that the electrons in the outer shell are further away from the nucleus, and so the attraction decreases and it is easier for the atom to lose electron, thus becoming more reactive, as is the case for group 1 (the alkali metals).
However, as you go down group 7 (the halogens), reactivity actually decreases, and the reason given is that it is harder for it to gain electrons, which contradicts the previous statement? Any ideas?
I'm guessing that because halogens only need 1 more electron to complete their shell; they need to be small (to have a strong attraction between the nucleus and the electrons) and vise versa for the alkali metals.
P.S. Please keep answers brief and generalise as much as possible. The answer need only be correct to a GCSE standard, thanks.