Class 12 Chemistry - Chapter The Solid State NCERT Solutions | Ionic solids, which have anionic vacanci

Welcome to the NCERT Solutions for Class 12th Chemistry - Chapter The Solid State. This page offers a step-by-step solution to the specific question from Exercise 1, Question 22: ionic solids which have anionic vacancies due to....
Question 22

Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.

Answer

The colour develops because of the presence of electrons in the anionic sites. These electrons absorb energy from the visible part of radiation and gets excited.

For example, when crystals of NaCl are heated in an atmosphere of sodium vapours, the sodium atoms get deposited on the surface of the crystal and the chloride ions from the crystal diffuse to the surface to form NaCl with the deposited Na atoms. During this process, the Na atoms on the surface lose electrons to form Na+ ions and the released electrons diffuse into the crystal to occupy the vacant anionic sites. These electrons get excited by absorbing energy from the visible light and impart yellow colour to the crystals.

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