Question

The number of carbon atoms per unit cell of diamond is:
(NEET-UG – 2013)

• A. $6$
• B. $4$
• C. $8$
• D. $1$

Answer 1

The correct option is C $8$

Carbon particles occupy half of tetrahedral voids and occupy fcc sites.
Thus, there are eight corner atoms, six face center and four more atoms inside the structure (tetrahedral voids).

$\therefore$ No. of atoms contributed by the corner atoms to an unit cell is $\frac{1}{8}\times 8=1$

No. of atoms contributed by the face centred atoms to the unit cell is $1/2\times 6=3$
And atoms in tetrahedral voids $=4$

Thus, total number of carbon atoms present in a diamond cubic unit cell is $1+3+4=8$

Hence, option (c) is correct.