Question

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

Answer 1

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Solution:

i. C atoms are present at the 8 corners. The contribution of each corner atom to the unit cell is 1/8 atom. Hence, the number of C atom that belongs to the unit cell = 8×(1/8)

= 1

ii. D atoms are present at the centres of six faces of unit cell. Each face-centre atom is shared between two cubes. Hence, centribution of each face centre atom to the unit cell is 1/2 atom.

The number of D atoms that belong to unit cell = 1/2×6 =3There are one C atom and three D atoms in the unit cell.

∴ Formula of compound = CD3