Chemistry

Problem

The lattice energy of MgO is substantially larger than that of NaF. Suppose the

\mathrm{Mg}^{2+}

ions in MgO (ionic radius

\approx 72\,\text{pm}

) were hypothetically replaced by

\mathrm{Ca}^{2+}

ions (ionic radius

\approx 100\,\text{pm}

) while the

\mathrm{O}^{2-}

sublattice remained unchanged. Which prediction about the modified compound is most consistent with Coulomb’s law? a) The magnitude of the lattice energy would be larger because the compound now contains a heavier cation. b) The magnitude of the lattice energy would be unchanged because the charges on the ions are the same. c) The magnitude of the lattice energy would be smaller because the cation–anion distance increases. d) The magnitude of the lattice energy would be larger because the larger

\mathrm{Ca}^{2+}

ion presents more surface area for attraction to

\mathrm{O}^{2-}

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