Problem: The ionic compound CaO crystallizes with the same structure as sodium chloride. In this structure, how many O2− are in contact with each Ca2+ ion (Hint: Remember the pattern of ions shown in the figure repeats over and over again in all three directions.)

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The ionic compound CaO crystallizes with the same structure as sodium chloride.

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 4 Group 1A K 2.03 and K+ 1.52.  Period 5 Group 1A Rb 2.20 and Rb+ 1.66. Period 2 Group 2A contains Be 0.96 and Be2+ 0.59.  Period 3 Group 2A contains Mg 1.41 and Mg2+ 0.86. Period 4 Group 2A contains Ca 1.76 and Ca2+ 1.76.  Period 5 contains Sr 1.95 and Sr2+ 1.32. Period 2 Group 3A contains B 0.84 and B3+ 0.41.  Period 3 Group 3A contains Al 1.21 and Al3+ 0.68.  Period 4 contains Ga 1.22 and Ga3+ 0.76.  Period 5 contains In 1.42 and In3+ 0.94. Period 2 Group 6A contains O 0.66 and O2- 1.26. Period 3 Group 6A contains S 1.05 and S2- 1.70. Period 4 contains Se 1.20 and Se2- 1.84.  Period 5 Te 1.38 and Te2- 2.07. Period 2 Group 7A contains F 0.57 and F- 1.19.  Period 3 Group 7A contains Cl 1.02 and Cl- 1.67.  Period 4 contains Br 1.20 and Br- 1.82. Period 5 I 1.39 and I- 2.06.

In this structure, how many O2− are in contact with each Ca2+ ion (Hint: Remember the pattern of ions shown in the figure repeats over and over again in all three directions.)

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