ChemistryChapter 12: Halogens
Halogen Physical Trends — Volatility
Volatility of the halogens is how readily X₂ enters the vapour phase.
Learning objectives
- Explain Halogen Physical Trends — Volatility using Group 17 language.
- Link trends to size, shielding, forces and bond strength.
- Apply equations and observations in FBISE-style answers.
Definition
Volatility of the halogens is how readily X₂ enters the vapour phase. Down Group 17, London forces between larger molecules strengthen, boiling points rise, and volatility falls: F₂ and Cl₂ are gases, Br₂ a volatile liquid, I₂ a solid that sublimes.
Core Concept
Volatility ↓ down Group 17 bp ↑ because London ↑ with size/polarizability F₂, Cl₂ gases · Br₂ volatile liquid · I₂ sublimes Parent topic: Halogen Physical Trends
Beginner
Volatility = how easily it becomes vapour. Down the halogen group, they stick together more, so volatility goes down. Gases → liquid → solid (that can sublime).
Intermediate
Tie volatility explicitly to boiling point and London forces. Quote rtp states. Mention I₂ sublimation as the named solid behaviour.
Advanced
Volatility contrasts condensed-phase cohesion with the gas phase. Sublimation of I₂ shows significant vapour pressure of the solid without denying low volatility relative to F₂/Cl₂.
Remember
London↑ → bp↑ → volatility↓ · F₂/Cl₂ gas · Br₂ liquid · I₂ solid/sublimes · parent: physical trends.
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Halogen Physical Trends — Volatility
Sticky Notes · Quick Revision
Trend
- volatility decreases down group
- bp increases
- London forces up
States
- F₂ Cl₂ gases
- Br₂ liquid
- I₂ solid / sublimes
Reason
- larger molecules
- more polarizable
- stronger London
Parent aliases
- halogen physical trends
- volatility
- group 17 boiling points
60-second revision
- Volatility falls down Group 17 as London forces and boiling points rise.
- F₂/Cl₂ gas, Br₂ liquid, I₂ solid (sublimes).
- Intermolecular story only.
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