Question

A unit cell consists of a cube in which there are anions at each corner and one at the center of the unit cell. The cations are the center of the each face. How many

(A) cations and

(B) anions make up the unit cell

(C)What is the simplest formula of the compound ?

Answer 1

(A) The cation at the center of each face is shared by two unit cells. Hence no. of cations= 6 X 1/2 = 3

(B) The anion at each corner is shared by 8 unit cells . the anion at the center is not shared by any other unit cell. Hence no. of anions= 8 X 1/8 + 1 = 2

(C) Since there are 3 cations and 2 anions the simplest formula of the compound is A₃B₂.