1. Metals (like alkali metals)
- Reactivity increases down the group.
- Outer electrons are farther from the nucleus → easier to lose.
- Example: Li < Na < K < Rb < Cs
2. Nonmetals (like halogens)
- Reactivity decreases down the group.
- They gain electrons, but outer electrons are farther away → harder to attract.
- Example: F > Cl > Br > I
3. Oxygen family (O, S, Se…)
- Nonmetals: Reactivity decreases down the group.
Simple rule:
- Metals → more reactive down
- Nonmetals → less reactive down