Question

In silver bromide crystal, the ion size lies in the order \[A{{g}^{+}} << B{{r}^{-}} \] The silver bromide crystal should have the following characteristics
A) Defectless (perfect) crystal
B) Schottky defect only
C) Frenkel defect only
D) Both Schottky and Frenkel defects

Answer 1

Hint: The various defects in crystal lattice arise due to the missing of cation and anion from the crystals which causes vacant sites. In silver bromide if the size of the silver ion is smaller than bromine ion then only silver ions create the defect.

Complete Step by Step Answer:
In silver bromide crystals if the size of the silver cation is much less than the size of the bromide ion then the silver cation leaves its position and occupies the interstitial site of the silver bromide crystal. This defect is called the Frankel defect.

The major characteristics of the Frankel defect are:
- In this defect there is a very large difference in size between cation and anion.
- In this defect either cation or anion leave the solid crystal.
- Atoms or the ions do not move out of the crystal permanently in this defect.
- Here generally one vacancy is formed.
- The density of the solid remains the same.
Thus in silver bromide crystal, the ion size lies in the order \[A{{g}^{+}} << B{{r}^{-}} \] The silver bromide crystal should have the following characteristics due to Frenkel defect only.
Thus the correct option is C.

Note: The crystal solid like sodium chloride, silver bromide, potassium chloride, silver iodide, zinc sulphide show Frankel defect by the removal of corresponding cation or anions. Due to the Frankel defect the crystal lattice gives colour.