CHEMISTRY CLASS 12, Chapter 1 Solid States Class 12 Chemistry, Chapter 1 Solid States | Page 36

Non-Stoichiometric Defects
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Nonstoichiometric inorganic solids contain the constituent elements in a non-stoichiometric ratio due to defects in their crystal structures.
These defects are of two types:( i) metal excess defect and( ii) metal deficiency defect.
( i) Metal Excess Defect.
o Metal excess defect due to anionic vacancies: o This type of defect is exhibited by alkali halides like NaCl and KCl.
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Application of heat to NaCl in an atmosphere of sodium vapour results in deposition of the sodium atoms on the surface of the crystal.
o The sodium atoms lose electron to form Na +
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The Cl – ions diffuse to the surface of the crystal and combine with Na atoms to give NaCl.