Problem: In the ionic compounds LiF, NaCl, KBr, and RbI, the measured cation-anion distances are 2.01 Å (Li - F), 2.82 Å (Na - Cl), 3.30 Å (K - Br), and 3.67 Å (Rb - I), respectively.What estimates of the cation-anion distance would you obtain for these four compounds using neutral atom bonding atomic radii?

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In the ionic compounds LiF, NaCl, KBr, and RbI, the measured cation-anion distances are 2.01 Å (Li - F), 2.82 Å (Na - Cl), 3.30 Å (K - Br), and 3.67 Å (Rb - I), respectively.

Period 2 Group 1A contains Li 1.28 and Li cation 0.90.  Period 3 Group 1A Na 1.66 and Na+ 1.16.  Period 3 Group 1A K 2.03 and K+ 1.52.  Period 4 Group 1A Rb 2.20 and Rb+ 1.66.Period 1 Group 2A contains Be 0.96 and Be2+ 0.59.  Period 2 Group 2A contains Mg 1.41 and Mg2+ 0.86. Period 3 Group 2A contains Ca 1.76 and Ca2+ 1.76.  Period 4 contains Sr 1.95 and Sr2+ 1.32. Period 1 Group 3A contains B 0.84 and B3+ 0.41.  Period 2 Group 3A contains Al 1.21 and Al3+ 0.68.  Period 3 contains Ga 1.22 and Ga3+ 0.76.  Period 4 contains In 1.42 and In3+ 0.94. Period 1 Group 6A contains O 0.66 and O2- 1.26. Period 2 Group 6A contains S 1.05 and S2- 1.70. Period 3 contains Se 1.20 and Se2- 1.84.  Period 4 Te 1.38 and Te2- 2.07. Period 1 Group 7A contains F 0.57 and F- 1.19.  Period 2 Group 7A contains Cl 1.02 and Cl- 1.67.  Period 3 contains Br 1.20 and Br- 1.82.  Period 4 I 1.39 and I- 2.06.

What estimates of the cation-anion distance would you obtain for these four compounds using neutral atom bonding atomic radii?

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