CAIE A Level Chemistry 9701 · Group 17
The table shows the boiling points and bond dissociation energies of chlorine, bromine and iodine.
| Halogen | Colour | Boiling point / °C | Bond dissociation energy / kJ mol⁻¹ |
|---|---|---|---|
| pale green | –34 | 242 | |
| red-brown | 59 | 193 | |
| dark grey | 184 | 151 |
Explain the trend in volatility (boiling point) and the trend in bond strength shown in the table. In your answer refer to the colours of the halogens, the intermolecular forces between the molecules, and the bonding within the molecules.
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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