The big idea: A more reactive halogen will displace (kick out) a less reactive halogen from its compound.
Think of it like a competition:
- Chlorine is more reactive than bromine
- So chlorine can steal electrons that bromine was holding
- Chlorine takes the metal, bromine gets kicked out
Example: Chlorine + potassium bromide → potassium chloride + bromine
Cl₂ + 2KBr → 2KCl + Br₂
Chlorine displaces bromine because Cl is MORE reactive than Br
What you'd observe:
- Solution changes from colourless to orange/brown (bromine is released)
Will it react?
- Chlorine + bromide → YES (Cl more reactive)
- Chlorine + iodide → YES (Cl more reactive)
- Bromine + chloride → NO (Br less reactive than Cl)
- Iodine + bromide → NO (I less reactive than Br)
Quick Check: Bromine solution is added to potassium iodide solution. State whether a reaction occurs and describe what you would observe.
A reaction does occur because bromine is more reactive than iodine. Bromine displaces iodine from the potassium iodide. The solution turns brown/dark brown as iodine is released: Br₂ + 2KI → 2KBr + I₂.
This key facts covers Halogen Displacement Reactions within Group 7: Halogens for GCSE Chemistry. Revise Group 7: Halogens in Atomic Structure for GCSE Chemistry with 22 exam-style questions and 21 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Group 7: Halogens
How many electrons do halogens have in their outer shell?
Explain why chlorine is more reactive than bromine.