1. Metals (left side of periodic table)
- Reactivity increases down a group → bigger atoms lose electrons more easily.
- Example: Lithium < Sodium < Potassium.
- Reactivity decreases across a period → atoms hold onto electrons more tightly.
- Stability: Less reactive metals are more stable (like gold).
2. Nonmetals (right side of periodic table)
- Reactivity decreases down a group → bigger atoms find it harder to gain electrons.
- Example: Fluorine > Chlorine > Bromine.
- Reactivity increases across a period → smaller atoms gain electrons more easily.
- Stability: Elements are most stable when they have a full outer shell (like noble gases).
Key point:
- Metals want to lose electrons, nonmetals want to gain electrons.
- Reactivity depends on how easily they can do that.