Consider the ionic compounds KF, NaCl, NaBr, and LiCl.

(a) Use ionic radii (Figure 7.8) to estimate the cation–anion distance for each compound.

(b) Based on your answer to part (a), arrange these four compounds in order of decreasing lattice energy.

(c) Check your predictions in part (b) with the experimental values of lattice energy from Table 8.2. Are the predictions from ionic radii correct?

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Group 1A Group 2A Group 3A Group 6A Group 7A Li+ 0.90 Be2+ 0.59 B3+ 0.41 02- F- 1.26 1.19 Li Be 0.96 B 0.84 1.28 0.66 0.57 Na* 1.16 Mg2+ 0.86 AP+ 0.68 s2- 1.70 1.67 Na 1.66 Mg 1.41 Al 1.21 S 1.05 CI 1.02 K+ 1.52 Ca2+ 1.14 Ga3+ 0.76 Se2- 1.84 Br 1.82 K 2.03 Са 1.76 Ga Se 1.20 Br 1.20 1.22 Rb+ 1.66 Sr2+ 1.32 In3+ 0.94 Te2- 2.07 I- 2.06 Rb 2.20 Sr 1.95 In 1.42 Te 1.38 I 1.39