Question

When cadmium oxide reacts to form cadmium selenide, a change in unit cell occurs, as depicted below: (a) What is the change in unit cell? (b) Does the coordination number of cadmium change? Explain.

Short answer

Cadmium oxide reacts to form Cadmium Selenide:

1. The unit cell changes from NaCl type structure to ZnStype structure
2. The coordination number of Cd²⁺ changes from 6 to 4

Step-by-step solution

NaCl type structure

In NaCl, the crystal lattice is ccp type packed, where the chloride ions are arranged in FCC array and the sodium ions are arranged in all the octahedral sites of the lattice. In this lattice, each sodium atom is surrounded by the six chlorine atoms and vice-versa.

ZnS type structure

Zinc blende has a face-centered cubic unit cell, where the sulfur ions are present in FCC array and the zinc ions are arranged in alternate octahedral sites. The coordination number herein is 4.

When CdO converts to CdS

When cadmium oxide (CdO) reacts to form cadmium sulphide (CdS), the crystal structure changes from NaCl type structure to ZnS type structure. Hence, the coordination number changes from 6 to 4.