Question

How many atoms are present in hcp per unit cell?

• A. 4
• B. 2
• C. 1
• D. 6

Hint:

In hcp unit cells, consider the contributions from corner atoms, face-centered atoms, and any atoms entirely within the unit cell when calculating the total number of atoms.

Answer 1

The Correct Option is D

In a hexagonal close-packed (hcp) unit cell, there are: - 12 atoms on the corners of the hexagon, each shared by 6 unit cells, contributing \( \frac{1}{6} \) per corner atom. - 2 atoms in the face centers, each shared by 2 unit cells, contributing \( \frac{1}{2} \) per face-centered atom. - 2 atoms entirely within the unit cell. Thus, the total number of atoms per unit cell is: \[ \text{Total atoms} = 12 \times \frac{1}{6} + 2 \times \frac{1}{2} + 2 = 6 \] Therefore, there are 6 atoms per unit cell in an hcp structure.