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Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain

Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain

Grade:12th pass

1 Answers

Pawan Prajapati
askIITians Faculty 60787 Points
3 years ago
Let us take an example of NaCl. When NaCl crystal is heated in presence of Na vapour, some Cl–ions leave their lattice sites to combine with Na to form NaCl. The e-1 s lost by Na to form Na+ (Na+ + Cl–—> NaCl) then diffuse into the crystal to occupy the anion vacancies. These sites are called F-centres. These e-s absorb energy from visible light, get excited to higher energy level and when they fall back to ground state, they impart yellow colour to NaCl crystal.

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