The Solid State

Short Answer Type

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Explain the following term with suitable examples:
'Frenkel defect'

It is a type of vacancy defect. In ionic compounds, some of the ions (usually smaller in size) get dislocated from their original site and create defect. This defect is known as Frenkel Defects. Since this defect arises because of dislocation of ions, thus it is also known as Dislocation Defects. As there are a number of cations and anions (which remain equal even because of defect); the density of the substance does not increase or decrease.

Ionic compounds; having large difference in the size between their cations and anions; show Frenkel Defects, such as ZnS, AgCl, AgBr, AgI, etc. These compounds have smaller size of cations compared to anions.

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    Long Answer Type

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    Short Answer Type

    Examine the illustration of a portion of the defective crystal given below and answer the following questions:
    (i) What are these types of vacancy defects called?
    (ii) How is the density of a crystal affected by these defects?
    (iii) Name one ionic compound which can show this type of defect in the crystalline state.
    (iv) How is the stoichiometry of the compound effected?


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