Question

there are 3 ionic compounds, 1st has fcc lattice of anions and cations are present at all tetrahedral voids , 2nd has fcc lattice and of anions and cations are present in all octahedral voids and 3rd compound has simple cubical lattice in which cubical void is occupied by cation then the order of packing efficiency will be ? a) 1>2>3 b) 2>1>3 c) 3>2>1 d) 3>1>2 the given answer is c. can anyone explain why ?

Answer 1

Answer:

Since packing efficiency of various crystal systems are

Crystal System Packing Efficency

FCC 74%

Simple Cubic 52.4%

Now, number of tetrahedral voids =2× Number of octahedral voids.

Since the crystal system (III) is a simple cubic lattice, it will have the least packing efficiency.

Now, both crystal systems I and II are FCC but the number of voids is filled in crystal system I than II because of a greater number of tetrahedral voids than octahedral voids. So, crystal system I have the most packing efficiency.

Explanation:

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