The Solid State

Question 41

Define non-stiochiometry defect in crystals?

Those defect which lead to change in composition of solids are called non-stoichiometric defects.They are most often inorganic compounds, and almost always solids They contain constituting particles in non-stoichiometric ratio, e.g., Fe0.93 O1.0, Ni0.94 O1.0 are examples of non-stochiometric compounds.
Question 42

What is the arrangement of Zn2+ and S2– ions in Zinc blende (ZnS) crystal structure?

Zinc sulfide crystallizes in a Face-Centered Cubic unit cell (FCC) having an edge length of 5.409 Angstroms
Sulfide anions have FOUR neighbors of opposite charge arranged at vertices of a tetrahedron. Zinc cations also have FOUR neighbors of opposite charge arrange at vertices of a tetrahedron. So the Zn : S coordination ratio is 4 : 4 or 1 : 1.
Question 43

explain the effect of Frenkel structural defect on the electrical conductance of a crystalline solid?

Frenkel Defect: This defect is shown by ionic solids. The smaller ion (usually cation) is dislocated from its normal site to an interstitial site . It creates a vacancy defect at its original site and an interstitial defect at its new location. this vacancy defect increase the Electrical conductance.
Question 44

An ionic compound AB2 possess CaFtype crystal structure. What the co-ordination number of A2+ and B ions in crystal of AB2 explain.

CaF is partof bcc inwhich the Ca2+ is located at the body centred Fis located atthe corners of the unit cell thus co-ordination numberof Ca2+ is 8 and co-ordination number of Fis 4. similarly in AB  The co-ordination number of A2+ is 8, whereas B- ion co-ordination number is 4.

NCERT Book Store

NCERT Sample Papers

Entrance Exams Preparation