Question

An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of the faces of the cube. The empirical formula for this compound would be ______.

Options

• A₃B

• AB₃

• A₂B

• AB

Answer 1

An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of the faces of the cube. The empirical formula for this compound would be AB₃.

Explanation:

A ions at 8 corners. Each corner atom is shared by 8 unit cells.

= `8 xx 1/8`

= 1 A ion

B ions at 6 face centres. Each face-centered atom is shared by 2 unit cells.

= `6 xx 1/2`

= 3 B ions

A : B = 1 : 3

∴ Empirical formula = AB₃