Ionic solids having crystal defects develop colour.explain the colour of KCl as violet and ZnO as yellow on the basis of crystal defects
Answers
Explanation:
Metal excess defects are seen because of missing of anions from regular site leaving a hole which is occupied by electron to maintain the neutrality of the compound. Hole occupied by electron is called F-centre and responsible for showing colour by the compound.
This defect is common in NaCl, KCl, LiCl, etc. Sodium atoms get deposited on the surface of crystal when sodium chloride is heated in an atmosphere of sodium vapour. In this process, the chloride ions get diffused with sodium ion to form sodium chloride and sodium atom releases electron to form sodium ion. This released electron gets diffused and occupies the anionic sites in the crystal of sodium chloride; creating anionic vacancies and resulting in the excess of sodium metal.
vacancy defects
The anionic site occupied by unpaired electron is called F-centre. When visible light falls over the crystal of NaCl, the unpaired electron present gets excited because of absorption of energy and impart yellow colour. Because of similar defect if present, crystal of LiCl imparts pink colour and KCl imparts violet.
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