3a2 Modern Periodic Table

Metals on the left and centre, non-metals on the right.

The pattern of reactivity changes down the group is different for the metals and the non-metals but this is not just being awkward, it depends on the kind of reaction that metals and non-metals do.

Metals usually react by losing one or more electron(s) to form positive ions.
Non-metals usually react by gaining one or more electron(s) to form negative ions.

A reactive metal is one which can lose electron(s) easily.
A reactive non-metal is one which can gain electron(s) easily.

Electrons are held most tightly when they are close to the nucleus.

Small atoms have a strong pull on their electrons.
Large atoms have a weak pull on their electrons.

A small metal atom hangs on tightly to its electrons and so is UNREACTIVE.
A large metal atom hangs on weakly to its electrons and so is REACTIVE.
Reactivity of metals increases down the group.

A small non-metal atom attracts electrons really strongly and so is REACTIVE.
A large non-metal atom attracts electrons weakly and so is UNREACTIVE.
Reactivity of non-metals decreases down the group.