How many atoms contribute to a simple cubic unit cell?

• A. 2
• B. 1
• C. 4
• D. 8

Answer: (B)

In a simple cubic unit cell, atoms sit at the eight corners of the cube. Each corner atom is shared by eight neighboring unit cells, so only one-eighth of each corner atom belongs to a given cell. With eight corners, the total contribution is 8 × (1/8) = 1 atom per unit cell. This is why the simple cubic arrangement has one atom per cell. (Other lattice types add atoms differently, but the simple cubic case is just the corner contributions.)