CAIE A Level Chemistry 9701 · Chemical energetics
The table shows the ionic radii of three Group I ions and the numerical values of their enthalpy changes of hydration, .
| Ion | Ionic radius / pm | / kJ mol |
|---|---|---|
| Li | 76 | 519 |
| Na | 102 | 406 |
| K | 138 | 322 |
Describe the trend in the numerical magnitude of shown by these ions, and explain the trend in terms of the factors affecting the strength of the ion–water attraction.
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.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.