Why Does Reactivity Differ in Group 7?

[Biele]

TL;DR

why does group 7 go down in reactivity even though electron shielding still increases further down the group which is the same as the other groups

ik this is basic knowledge, that all groups go up in reactivity the further down you go in the group, except for group 7, where this is reversed.

however i don't understand why, because in group 7, the electron shielding still increases the further down the group you go, like with all the other groups and usually more electron shielding = increased reactivity. so can someone explain why this is different in group 7? sorry I'm really trying to understand chemistry as best I can.

 

[chemisttree]

What is meant by “reactivity”?

 

[DrJohn]

Which groups react by gaining an electron and which react by loosing an electron?
Then ask yourself:
Will it be easier or harder as you go down a group to do this?