Question

If $Z$ is the number of atoms in the unit cell that represents the closest packing sequence .....ABCABC......, the number of tetrahedral voids in the unit cell is equal to :

• A. Z
• B. 2Z
• C. Z/2
• D. Z/4

Answer 1

Answer: (B)

2Z

In cubic closed pack system (CCP system) .......ABC ABC....... type of arrangement of layers is found. In this system, there are atoms at the corners as well as centre of the unit cell.
$\therefore$ No. of atoms per unit cell $=8\times \frac{1}{8}+1=2$
Hence, the no. of tetrahedral voids in a unit cell $=2Z$