The lattice energy of an ionic compound increases when
- A. the charges on the ions increase and their radii decrease
- B. the charges on the ions decrease
- C. the ions become larger
- D. the compound is dissolved in water
Explanation
Electrostatic attraction is proportional to the product of the charges and inversely proportional to the distance between the ion centres, so small, highly charged ions pack closely and bind strongly. This is why magnesium oxide, with 2+ and 2- ions, has a far higher lattice energy and melting point than sodium chloride. Dissolving the compound breaks the lattice rather than strengthening it.