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  • Match the types of defect given in Column I with the statement given in Column II. (i) Impurity defect

Match the types of defect given in Column I with the statement given in Column II.

 

Column I Column II
(i) Impurity defect (a) NaCl with anionic sites called F-centres
(ii) Metal excess defect (b) FeO with Fe^{3+}
(iii) Metal deficiency defect (c) NaCl with Sr^{2+} and some cationic sites vacant

 

Answers (1)

i) —>(c); (ii) —>(a); (iii) —> (b)
(A) (i) Impurity defects: The defects introduced in the crystal lattice due to presence of the certain impurity are called impurity defects.
Example: Substitution of Na^{+}ions in NaCl by Sr^{2+} ions.
Structure with defect:
 
Impurity defect due to substitution of Na^{+} ions in NaCl by Sr^{2+} ions (Cation vacancy) ‘Schottky Defect’


(B) On heating NaCl in vapour of sodium, some of the Cl ions leave their lattice site and create anion vacancies. For chloride ions to combine with sodium vapour to form sodium chloride, sodium atom loses electrons to form Na^{+} ions. This released electron on  diffusion into the crystal gets entrapped in the anion vacancy called F-centre.

 
(C) Metal deficiency is caused when a cation is missing from its lattice site and a nearby metal ion acquires 2 positive charge to maintain electrical neutrality.
This type of defect can be seen in compounds where metal exhibit variable valency.
Example: FeO, FeS, NiO

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