The unit cell of sodium chloride is
Correct answer: D. face centred cubic
- A. simple cubic
- B. hexagonal
- C. body centred cubic
- D. face centred cubic
Explanation
Sodium chloride crystallises in a face centred cubic arrangement in which each sodium ion is surrounded octahedrally by six chloride ions and each chloride by six sodium ions, giving a coordination number of six for both. Caesium chloride, whose larger cation allows eight neighbours, adopts a body centred arrangement instead. The unit cell is simply the smallest repeating block from which the whole lattice can be built.
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About Shape of Ionic Crystals
Ionic crystal shape depends on the regular arrangement of oppositely charged ions in a three-dimensional lattice. The topic covers coordination number, radius ratios, lattice geometry and structures such as sodium chloride, caesium chloride and zinc sulfide, which should not be confused with the molecular shapes predicted by VSEPR theory.
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