Question

A unit cell consists of a cube in which there are anions Y at each corner and cations X at the centre of alternate faces of the unit cell. What is the simplest formula of the compound?

Answer 1

Contribution of an atom placed at corner of the unit cell is 1/8

Therefore the total no. of anion (Y)which are present in a unit cell is = 1/8 *total no. of corners= (1/8)* 8 =1 anion

Contribution of an atom placed at face centre = 1/2

When cations are placed at the alternative faces the total no of face centred atoms are 2.

therefore total no. of cations are = 1/2 * 2= 1

thus the formula of compound is XY.