(a) How are tetrahedral and octahedral holes created ? (b) Is there any difference between cubic closed packed and face-centred cubic structure ? What is the other notation for such structures ? (c) Which type of substances show Schottky defect ? Give two examples of substances showing this defect.

(a) How are tetrahedral and octahedral holes created ? (b) Is there a

1.	(a) How are tetrahedral and octahedral holes created ? (b) Is there any difference between cubic closed packed and face-centred cubic structure ? What is the other notation for such structures ? (c) Which type of substances show Schottky defect ? Give two examples of substances showing this defect.
Answer» Solution :(a) When a sphere in the second layer is above the voids in the FIRST layer, a TETRAHEDRAL hole is CREATED. When the triangular void in the second layer is above the triangular void in the first layer, an octahedral void is created. (b) There is no difference between cubic closed packed and face-centred cubic STRUCTURES. These are also represented as ABCABC... structures. (c) Ionic substances show Schottky defect. NaCl and KCl are EXAMPLES of substances with this defect.