Question

What is the effect of Frenkel defect on the density of ions solids?
(a) The density of the crystal increases.
(b) The density of the crystal decreases.
(c) The density of the crystal remains unchanged.
(d) There is no relationship between density of a crystal and defect present in it.

Answer 1

Hint: Defects are the irregularities in the arrangement of constituent particles. It can be classified into two types:
(a) Point defects: Irregularities around a point or an atom in a crystalline substance.
(b) Line defects: Irregularities from ideal arrangement in entire rows of the lattice point.

Complete step by step solution:

Point defects can be further classified into:
(a) Stoichiometric defects
(b) Impurity defects
(c) Non- stoichiometric defects

Frenkel defects come under stoichiometric defects, stoichiometric defects occur when there is no disturbance in the stoichiometry of the solid i.e. there is no change in the ratio of number of positive and negative ions.

Now stoichiometric defects can also be further classified into:
(a) Vacancy defect
(b) Interstitial defect
(c) Frenkel defect
(d) Schottky defect
Frenkel defect is shown by ionic solids and it should always maintain electrical neutrality.
Frenkel defect is also called dislocation defect and it is a type of point defect in crystalline solids. This defect occurs when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy defect at its original site and an interstitial defect at its new site.
There is no change in the density of the solid, thereby the mass and the volume of solid is conserved.
In the Frenkel defect, there is a large difference between the size of the ions, for example ZnS, AgCl, AgBr and AgI , the size of \[A{{g}^{+}}\] and \[Z{{n}^{2+}}\] ions are small.

From the above points we can conclude that density of the ionic solids does not change due to Frenkel defect. Therefore, the correct answer to the question is option (d).

Note: Vacancy and interstitial defects are shown by non-ionic solids.Vacancy defect occurs when atoms are missing from its lattice sites, creating a vacancy. There is a decrease in the density of the solid.Interstitial defect occurs when an atom occupies the interstitial site. This defect increases the density of the substance.