Group 7 Halogens – Properties, Reactions, Colours
Understanding Group 7 halogens is essential for mastering O Level Chemistry 5070 and IGCSE Chemistry 0620. These elements, including fluorine, chlorine, bromine, iodine, and astatine, exhibit unique properties and reactivity patterns that are crucial for exams and practical applications.
Physical Properties of Group 7 Halogens
All group 7 halogens have distinct physical states and colours:
- Fluorine: Pale yellow gas
- Chlorine: Greenish gas
- Bromine: Red-brown liquid
- Iodine: Grey-black solid
- Astatine: Rare, likely metallic
They all have relatively low melting and boiling points that increase down the group.
Reactivity and Trends in Group 7 Halogens
As you move down the group, the reactivity of group 7 halogens decreases. This trend is explained by the increasing atomic size and decreasing attraction for electrons:
- Chlorine displaces bromine and iodine from solutions
- Fluorine is the most reactive
- Reactivity trend: Cl > Br > I > At
When group 7 halogens react with metals, they form halide salts, releasing positive ions. For example:
2Na + Cl₂ → 2NaCl
Colors and Displacement Reactions
The colors of group 7 halogens are characteristic and useful in identification:
- Chlorine: Pale greenish yellow
- Bromine: Orange-brown
They can displace each other in solutions, with the strongest halogen displacing the weaker ones:
Cl₂ + 2KBr → 2KCl + Br₂ (bromine displaces chlorine)
Boiling Points and State
The boiling points of group 7 halogens increase down the group, from gases to liquids to solids:
- Fluorine: -188°C
- Chlorine: -34°C
- Bromine: 58.8°C
- Iodine: 184°C
They normally exist as diatomic molecules (X₂).
Learn with Videos and Resources
Additional Resources & Tips
- Past papers for O Level Chemistry 5070
- Notes on Group 7 Halogens
- Crash Course and Formula sheet
- Exam tips and live class details
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