CAIE A Level Chemistry 9701 · Group 17
Chlorine, bromine and iodine are all simple molecular substances. Their boiling points are –34 °C, 59 °C and 184 °C respectively.
Explain, in terms of structure and bonding, why the boiling point increases from chlorine to iodine.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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