Solid StateHard
Question
An ionic compound consists of only A+, B2+ and C3− ions. Which of the following option(s) is/are correct with respect to their possible structure?
Options
A.C3– ions form CCP, A+ ions occupy all octahedral voids and B2+ ions occupy half of the tetrahedral voids.
B.B2+ ions form HCP, A+ ions occupy all octahedral voids and C3– ions occupy half of the tetrahedral voids.
C.A+ ions occupy alternate corners of a simple cube, B2+ ions occupy the other corners of the cube and C3– ions occupy body centre of the cube.
D.B2+ ions form CCP, C3– ions occupy all the tetrahedral voids and A+ ions occupy all the octahedral voids.
Solution
(a) $Z_{C^{3 -}} = 4,Z_{A^{+}} = 4,Z_{B^{2 +}} = \frac{1}{2} \times 8 = 4$
Crystal is electrically neutral and hence, it is possible.
(b) $Z_{B^{2 +}} = 6,Z_{A^{+}} = 6,Z_{C^{3 -}} = \frac{1}{2} \times 12 = 6$
Crystal is electrically neutral and hence, it is possible.
(c) $Z_{A^{+}} = 4 \times \frac{1}{8} = \frac{1}{2},Z_{B^{2 +}} = 4 \times \frac{1}{8} = \frac{1}{2},Z_{C^{3 -}} = 1$
Crystal is negatively changed and hence, it is not possible.
(d) $Z_{B^{+}} = 4,Z_{C^{3 -}} = 8,Z_{A^{+}} = 4$
Crystal is negatively changed and hence, it is not possible.
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