Question

Examine the given defective crystal.

Answer the following questions:
(i) What type of stoichiometric defect is shown by crystal?
(ii) How is the density of the crystal affected by this defect?
(iii) What type of ionic substances show such defects?

Answer 1

A crystal or a crystalline solid refers to a solid material whose constituents are being arranged in a highly ordered microscopic structure, leading to the formation of a crystal lattice which extends in all directions.

Complete step by step answer
Crystal defect refers to the imperfections in the regular geometrical arrangement of atoms in a crystalline solid. The imperfections result from the deformation of a solid, high-energy radiation (like X-rays or neutrons) striking the solid or rapid cooling from high temperature. Now, let us answer each questions one by one:
(i) In the given defective crystal, it is clearly visible that an equal number of cations as well as anion is found to be missing from the interstitial site. Thus, this type of stoichiometric defect is known as Schottky defect which is a vacancy defect.
(ii) When some lattice sites are left vacant during the crystal formation, the defect is known as vacancy defect. Schottky defect is a vacancy defect that leads to the lowering of the density of the crystal as an equal number of cations as well as anion is missing from the interstitial site.
(iii) This type of defect is shown by the ionic substances in which the cations as well as anions are of almost same sizes. For instance: $NaCl,{\text{ }}KCl,{\text{ }}CsCl$

Note:
Never get confused between Schottky defect and Frenkel defect. In case of Schottky defect, the size difference between cation as well as anion is small and both cations and anions leave the crystal. On the other hand, Frenkel defect comprises ionic crystals in which anion is larger compared to cation and here only smaller sized cation leaves the lattice structure.