The Greedy Non-Metals
📖 The Greedy Non-Metals
Halogens are like magnets reaching for a missing piece. With 7 electrons, they're just 1 short of a full outer shell. The smaller the atom (fluorine, chlorine), the closer the outer shell is to the positive nucleus — like a stronger magnet that can pull harder. Iodine is like a weaker magnet: it's bigger, so the outer shell is further away, giving a weaker pull on that extra electron.
Chemistry glossary
- Will Br₂ + NaCl react?
- NO — bromine is less reactive than chlorine
Every halogen has 7 electrons in its outer shell — just ONE short of a full shell.
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🧠 Memory Aids
Group 7 order: "Fluorine Chlorine Bromine Iodine Astatine" — "Fast Cars Burn In Accidents" (F, Cl, Br, I, At).
States at room temperature: "Gas Gas Liquid Solid" for F₂, Cl₂, Br₂, I₂ — the only liquid element in the group is bromine (memorise this as the exception).
Displacement rule: "More reactive = can displace less reactive" — if you can remember the order F > Cl > Br > I (decreasing reactivity), you can work out any displacement question.
Group 7 vs Group 1: "Group 1 wants to LOSE (gets easier going down), Group 7 wants to GAIN (gets harder going down)" — opposite trends for opposite processes.
Quick Check: Explain why chlorine is more reactive than iodine.
Chlorine has fewer electron shells than iodine, so its outer shell is closer to the nucleus. The electrostatic attraction between the nucleus and an incoming electron is greater in chlorine. This means chlorine can gain an electron more easily than iodine, making it more reactive.
Now try it yourself
Quiz · Question 1 of 22
How many electrons do halogens have in their outer shell?
Tap an answer to check it
This topic in real past papers
Every real exam question we've found on group 7: halogens, with a full worked answer.