Examine the trends in lattice energy in Table 12.1. The value of the lattice energy becomes somewhat more negative on going from NaI to NaBr to NaCl, and all are in the range from −700 to −800 kJ/mol. Suggest a reason for the observation that the lattice energy of NaF (Δ_latticeU = −926 kJ/mol) is much more negative than those of the other sodium halides.

Data given in Table 12.1

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TABLE 12.1 Lattice Energies of Some Ionic Compounds Compound LiF LICI LiBr Lil NaF NaCl NaBr Nal KF KCI KBr KI Alattice U (kJ/mol) -1037 -852 -815 -761 -926 -786 -752 -702 -821 -717 -689 -649