Question

A compound made of elements C and D crystallizes in a fee structure. Atoms of C are present at the corners of the cube. Atoms of D are at the centres of the faces of the cube. What is the formula of the compound?

Answer 1

1. C atoms are present at the 8 corners. The contribution of each corner atom to the unit cell is the `1/8` atom.
   Hence, the number of C atom that belongs to the unit cell = `8 × (1/8)` = 1
2. D atoms are present at the centres of the six faces of the unit cell. Each face-centre atom is shared between two cubes. Hence, the contribution of each face centre atom to the unit cell is a `1/2` atom.
   The number of D atoms that belong to the unit cell = `1/2 × 6` = 3
   There are one C atom and three D atoms in the unit cell.
   ∴ Formula of compound = CD₃