CAIE A Level Chemistry 9701 · Chemical energetics
The first electron affinities of the elements in Group 17 and Group 16 are shown in the table.
| Element | First electron affinity / kJ mol⁻¹ |
|---|---|
| F | –328 |
| Cl | –349 |
| Br | –325 |
| I | –295 |
| O | –141 |
| S | –200 |
| Se | –195 |
| Te | –190 |
Explain the trends in these values down each group and the reason why the first electron affinities of Group 16 elements are less exothermic than those of the corresponding Group 17 elements.
5 marks, so the mark scheme is looking for about 5 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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