Question

What is the coordination no of $Zn$ bend calcium in calcium chloriod, $Na$ & $O_2$ in sodium oxide.

Answer 1

There are four $Z{n}^{+2}$ ions and four $S^{-2}$ ions per unit cell as :

No. of $S^{-2}$ ions = 8(at corners) × 1/8 + 6(at face centres) × 1/2 = 4

No. of $Z{n}^{+2}$ ions = 4 (within the body) × 1 = 4

C.N of Zn in ZnS (zinc blend) is 4.

The unit cell of calcium chloride has 4 calcium and 4 chloride ions:

No of calcium ions = 12 (at edge centres) × 1/4 + 1 (at body centre) × 1= 4

No of chloride ions = 8(at corner) × 1/8+6(at face centres) × 1/2 = 4

Thus, C.N of Ca in CaCl is 4.

The unit cell of $N{a}_{2}O$ has 8 sodium and 4 oxygen ions:

No of sodium ions = 4 (at body centre) × 2= 8

No of oxygen ions = 6 (at face centres) × 1/2 = 3/4

Thus, C.N of Na in Na_2O is 4 and CN of O in Na_2O is 8.