Question

Number of carbon atoms per unit cell of diamond is ______.

• A. $4$
• B. $6$
• C. $8$
• D. $12$

Answer 1

Answer: (C)

$8$

Diamond has fcc unit cell structure made up of atoms.

This accounts for $8\times \frac{1}{8}+6\times \frac{1}{2}$ = 1 + 3 = 4 C atoms

C atoms are also present in one-half of the tetrahedral voids.

There are 8 tetrahedral voids in fcc structure.

This accounts for remaining $8\times \frac{1}{2}$ = 4 C atoms

Thus, total 4+4 = 8 C atoms are present per unit cell of diamond.