Specification Point 2.7:
Understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7
Halogens & Halides Displacement Reactions
Displacement Reaction: When a more reactive Halogen displaces a less reactive halogen for an aqueous solution of its halide.
- Reactivity of Group 7 non-metals increases as you go up the group
- Out of the 3 halogens, chlorine, bromine and Iodine, chlorine is the most reactive and iodine is the least reactive
Aqueous Solution Colour of Halogens:
If you add chlorine solution to colourless potassium solution, the solution becomes orange as bromine is formed. Chlorine is above bromine in group 7 so is more reactive. Chlorine will therefore displace bromine from an aqueous solution of metal bromide:
Chlorine + Potassium Bromide Solution → Potassium Chloride Solution + Bromine
2KBr (aq) + Cl2 (aq) → 2KCl (aq) + Br2(aq)
Bromine is above Iodine in Group 7 so is more reactive. Bromine will therefore displace Iodine from an Aqueous Solution of Metal Iodide:
Bromine + Magnesium Iodide Solution → Magnesium Bromide Solution + Iodine
Br2 (l) + 2MgI (aq) → 2MgBr (aq) + I2 (aq or s)
Specification Point 2.8C (Paper 2C Only):
Explain the trend in Reactivity in Group 7 in terms of Electronic Configurations
Electronic Configuration of Elements in Group 7
Trend in Reactivity of Group 7:
- Reactivity of group 7 non-metals increases as you go up.
- Each outer shell contains seven electrons and when group 7 metals react, they will need to gain one outer electron to get a full outer shell of electrons.
- As you go up group 7, the number of shells of electrons decreases (period number decreases up the Periodic Table).
- This means that the outer electrons are closer to the nucleus so there are stronger electrostatic forces of attraction that attracts the extra electron needed.
- This allows an electron to be attracted more readily, making it more reactive as you go up the group.
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Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.
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