Question

15. What is the simplest formula of the compound represented by the unit cell provided below? Large atoms: A, small dark atoms: B Hint: 4 of the B atoms are in faces of the unit cell. a. A2B b. AB2 c. AB4 d. AB e. A4B3

Answer 1

Ans : b) AB₂

Eight A atoms are present at the corners of the unit cells , and the contribution of each atom in the cell is 1/8. One A atom is present in the body center , so the total number of A atoms in the unit cell :

= 8(1/8) + 1

= 2 A atoms

Now 4 B atoms are present in the faces of unit cell , and the contribution of each atom in the cell is 1/2 . Two B atoms are present in the body center , so the total number of B atoms in the unit cell :

= 4(1/2) + 2

= 4 B atoms

the ratio of number of A : B atoms = 1 : 2

So the empirical formula will be AB₂