Recall: Lattice energy is the energy required to separate an ionic compound into its individual ions. It is given by:
where C = a constant that depends on the crystal structure of the ionic compound, Z+ = charge of the cation, Z– = charge of the anion, and Ro = interionic distance or the distance between the cation and anion.
The lattice energy of KF is 794 kJ/mol, and the interionic distance is 269 pm. The Na–F distance in NaF, which has the same structure as KF, is 231 pm. Which of the following values is the closest approximation of the lattice energy of NaF: 682 kJ/mol, 794 kJ/mol, 924 kJ/mol, 1588 kJ/mol, or 3175 kJ/mol? Explain your answer.