Group 17: reactions of the halogens and halides
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 practice questions, 6 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Chlorine in the swimming pool
- Physical properties down the group
Read the transcript of the teaching part
Last time
Before we start: last time, in Group 2 reactions and thermal decomposition, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Chlorine in the swimming pool
A swimming pool smells of chlorine, and the water stays clean. Chlorine kills bacteria, but it is also a toxic green gas. The halogens, chlorine, bromine and iodine, are the same family with the same chemistry, but the strength of their reactions changes in a clear, predictable pattern down the group.
Physical properties down the group
Chlorine is a green gas, bromine a red-brown liquid, and iodine a grey-black solid at room temperature. Iodine gives a purple vapour on heating. Volatility decreases down the group. The molecules have more electrons, so stronger instantaneous dipole-induced dipole forces, which need more energy to overcome. The X–X bond energy falls: 242 for chlorine, 193 for bromine, 151 for iodine kilojoules per mole. The atoms are larger, so the shared pair is further from the nuclei. Electronegativity falls too: 3.0, 2.8 and 2.5.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Chlorine with water and sodium hydroxide · Halide ions and concentrated sulfuric acid · Oxidising power and hydrogen halides.
Chapter 11: Group 17
- Group 17: reactions of the halogens and halides 9 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.