Question

The number of atoms per unit cell in a Body-Centered Cubic (BCC) structure is:

• A. 1
• B. 2
• C. 4
• D. 6

Hint:

Atoms per Unit Cell in Common Crystal Structures: Simple Cubic (SC) → 1 atom
Body-Centered Cubic (BCC) → 2 atoms
Face-Centered Cubic (FCC) → 4 atoms

Answer 1

The Correct Option is B

Concept: Crystalline solids consist of repeating three-dimensional arrangements of atoms called unit cells. The number of atoms present in a unit cell depends on how atoms are shared between neighboring cells. In a Body-Centered Cubic (BCC) structure:
• One atom is present at each of the eight corners of the cube.
• One atom is present at the center of the cube.

Step 1: Contribution of corner atoms. Each corner atom is shared by eight different unit cells. Therefore, contribution of each corner atom to one unit cell: \[ \frac{1}{8} \] Total contribution from eight corner atoms: \[ 8 \times \frac{1}{8} = 1 \]

Step 2: Contribution of body-centered atom. The atom present at the center of the cube belongs entirely to that unit cell. Contribution: \[ 1 \]

Step 3: Total atoms in BCC unit cell. \[ 1 + 1 = 2 \] Thus, the number of atoms per unit cell in a BCC structure is 2.