Q.1. Why are solids rigid ?
Ans:- Solids are rigid because the intermolecular forces of attraction that are present in solids are very strong. Their constituent particles have fixed positions and can only oscillate about their mean position.
Q.2. Why is glass considered a supercooled liquid ?
Ans:- Glass is an amorphous solid and has a tendency to flow, hence glass is considered as super cooled liquid.
Q.3. Write three differences between Crystalline solid and Amorphous solids ?
Ans:- Crystalline solid- (i) Definite geometrical shape.
(ii) Anisotropic in nature.
(iii) Long range order in arrangements of constituent particles.
Amorphous Solid-(i) Irregular shape.
(ii) Isotropic in nature.
(iii) only short range order in arrangement of constituent particles.
Q.4. What do you mean by point defect in a crystal ?
Ans:- Point defect in a crystal are caused by missing atom or ion in the crystal lattice that is deviation from regular arrangement of particles / ions in the crystal.
Q.5. Why is Franklin defect produced in solid crystal ?
Ans:- Franklin defect is produced by the dislocation of a smaller ion (using cations) from its normal site to an interstital site. it creates a vacancy at its original site and an interstitial defect at its new site. It is also called dislocation defect and increases with the increase in temperature.
Q.6. Write three differences between schottky defect and Frenkel defect ?
Ans:- Schottky defect- (i) When equal no. of cation and anion removed from crystal lattice.
(ii) It lowers the density of the crystal.
(iii) High coordination number.
Frenkel defect- (i) When one of cattion or anion occupy interstial site in lattice.
(ii) The density of the crystal is remains same.
(iii) Low coordination number.
Q.7. What are F – centres in a crystal ?
Ans:- A negative ion may be missing its lattice site leaving a holl which is occupied by an electron there by maintain the electrical balance. The sites containing by the electrons trapped in the anion vacancies are called F-centres.
Q.8. Why are ionic solids conduct electricity in the molten state and not in the solid state ?
Ans:- Ionic solids conduct electricity in the molten state because when ionic solid dissolved in water the ions become free to move. But in solid state ions are tightly packed so they are not free to move and not conduct electricity.
Q.9. What type of defect can arise when a solid is heated ? Which physical property is affected by it and in what way ?
Ans:- When a solid is heated, thus a vacancy defect is produced. The density of substance decreases, because some atoms or ions remove the crystal.
Q.10. What type of solids are electrical conductors, malleable and ductile?
Ans:- Cu , Fe solids are electrical conductors malleable and ductile.