How is reactivity related to an atoms outer shell?

The further away the outer shell from the nucleus of the atom, the lower the attractive forces between the positively charged nucleus and the negatively charged electrons in the outer shell.

• If we look at metals, it then gets easier for the atom to lose the outer shell electrons which is why the reactivity increases as you go down the group 1 and 2.
• For group 7 elements, this means it gets harder to gain electrons as we go down the group. Hence, the reactivity decreases.