Topic 1 · 13.1–13.2 · Free
Topic Notes · Easy summaries with diagrams
Chapter 13 — chapter 13
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📘Easy summary
Group 17 halogens: F, Cl, Br, I (At). They exist as diatomic non-polar molecules X₂ with ns² np⁵ configuration. At room temperature F₂ is a pale yellow gas, Cl₂ a greenish-yellow gas, Br₂ a red-brown liquid and I₂ a black-violet solid. Volatility decreases down the group because molecules get bigger, with more electrons, so London dispersion forces become stronger and boiling points rise; iodine has the strongest forces in the group and is solid. Bond energy of X₂: F₂ 156, Cl₂ 243, Br₂ 193, I₂ 151 kJ mol⁻¹. Bond energy decreases from chlorine to iodine as atoms get larger; fluorine is an exception — its very small atoms cause strong lone-pair repulsion, weakening the F–F bond.
⭐Key points
- Volatility decreases down.
- Stronger London forces down.
- Cl–Cl strongest; F–F weak.
🔬Diagram
🌿Real-life example
Bromine is the only liquid non-metal at room temperature.
💡Exam tip
- Explain F–F weakness by lone-pair repulsion.
✅Quick check
1. Strongest X–X bond:
2. Volatility down the group:
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