2.2.2Inorganic Chemistry
Group 7: Reactivity and Electronic Configurations — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions
5 min read 5 parts Lesson 17 of 23 Unit quiz
Part 1 of 5Electronic Configurations and Properties
The common outer shell makes the halogens a chemical family.
Outer shell
- Every halogen atom has seven electrons in its outer shell, so each needs just one more to complete it.
Examples
- Fluorine is 2,7, chlorine is 2,8,7, bromine is 2,8,18,7 and iodine is 2,8,18,18,7.
Molecules
- Halogens exist as diatomic molecules such as Cl₂, joined by a single covalent bond.
Ion formed
- They gain one electron to form halide ions with a 1− charge, for example Cl⁻.
Part 2 of 5Trend in Reactivity
Trend in Reactivity
Direction
- Reactivity decreases going down the group, so chlorine is more reactive than bromine, which is more reactive than iodine.
Distance
- In larger atoms the incoming electron is added to a shell further from the nucleus.
Shielding
- More inner shells shield the outer shell, so the nucleus attracts the extra electron less strongly.
Result
- The atom gains an electron less readily, so it is a weaker oxidising agent.
| Halogen | State at room temperature | Colour |
|---|---|---|
| Chlorine | Gas | Pale green |
| Bromine | Liquid | Red-brown |
| Iodine | Solid | Grey-black, purple vapour |
Part 3 of 5Displacement Reactions
Displacement Reactions
Principle
- A more reactive halogen displaces a less reactive halogen from a solution of its halide.
Chlorine and bromide
- Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq); the solution turns orange.
Chlorine and iodide
- Cl₂(aq) + 2KI(aq) → 2KCl(aq) + I₂(aq); the solution turns brown.
Bromine and iodide
- Br₂(aq) + 2KI(aq) → 2KBr(aq) + I₂(aq); bromine displaces iodine.
No reaction
- Iodine does not displace bromine or chlorine because it is less reactive.
Part 4 of 5Physical Trends
Physical Trends
Melting and boiling
- Melting and boiling points increase down the group because larger molecules have stronger intermolecular forces.
Colour
- The halogens get darker going down the group.
Reaction with hydrogen
- Reactivity with hydrogen decreasesfluorine reacts explosively even in the dark, iodine only slowly.
Part 5 of 5Exam Checklist & Tips
2.2.2 – Key Points for the Exam
- Halogen An element in Group 7 of the periodic table.
- Displacement A reaction in which a more reactive element takes the place of a less reactive one.
- Halide A compound or ion containing a halogen, such as bromide Br⁻.
- Diatomic Made of molecules containing two atoms.
Common Mistakes
- Saying halogens become more reactive down the group; reactivity decreases.
- Writing the halogen molecules as single atoms, for example Cl instead of Cl₂ in displacement equations.
- Confusing the trend with Group 1, where reactivity increases down the group.
- Predicting that iodine will displace bromine.
Last updated:
\n