Study Notes
Group 7, also known as the halogens, includes diatomic nonmetals like chlorine, bromine, and iodine, which show trends in colour and density as you move down the group. The reactivity of halogens decreases down the group due to the increased distance of the outer electrons from the nucleus, making it harder for them to gain electrons. A more reactive halogen can displace a less reactive one in an aqueous solution of its salt.
- Halogens — elements in Group 7 that are diatomic nonmetals. Example: Chlorine, bromine, and iodine.
- Reactivity Trend — reactivity decreases down the group. Example: Chlorine is more reactive than bromine.
- Displacement Reaction — a more reactive halogen displaces a less reactive one. Example: Chlorine displaces bromide ions in sodium bromide.
- Halide Ions — formed when halogens gain an electron. Example: Chloride ion (Cl⁻) from chlorine.
Exam Tips
Key Definitions to Remember
- Halogens are Group 7 diatomic nonmetals.
- Reactivity decreases down the group.
- Halide ions are formed when halogens gain an electron.
Common Confusions
- Confusing the trend of reactivity with density.
- Misunderstanding which halogen can displace another.
Typical Exam Questions
- What happens when chlorine reacts with sodium bromide? Chlorine displaces bromine, forming sodium chloride and bromine.
- Why does reactivity decrease down Group 7? The outer electrons are further from the nucleus, reducing attraction.
- What is the colour trend in Group 7? The colour becomes darker down the group.
What Examiners Usually Test
- Understanding of reactivity trends in Group 7.
- Ability to predict displacement reactions.
- Knowledge of physical properties like colour and state changes.