Question

A substance A’ crystallizes in fee lattice.

1. Calculate the number of atoms present per unit cell of ‘A’.

2. In a crystalline solid AB, some vacancy is produced by missing of equal number of oppositely charged ions. What is the defect called?

Answer 1

1. The number of atoms present per unit cell of ‘A’.

• Contribution from 8 corners = 1/8 × 8 = 1 
• Contribution from centres of 6 faces = 1/2 × 6 = 3
•  Total number of atoms of A’ per unit cell = 1 +3 = 4

2. Schottky defect