Q.1. What are fluids?
Ans. Liquids and gases which have ability to flow are called fluids.
Q.2. What is the cause of rigidity in solids?
Ans. The constituents particles in solids have fixed positions and can only oscillate about their mean position. This is cause of rigidity in solids.
Q.3. What kind of attractive forces are present in the molecular solids?Ans. Dipole-dipole interactions, London dispersion forces and hydrogen bonding.
Q.4. What kind of attractive forces are present in the ionic solids?Ans. Coulombic or electrostatic force of attraction. (Ionic bonding)
Q.5. What kind of attractive forces are present in the covalent solid?Ans. Covalent bonding.
Q.6. What kind of attractive forces are present in the metallic solids?
Ans. Metallic bonding.
Q.7. Are ionic solids electrical conductors or insulators?
Q.8. What are pseudo solids?
Ans. Amorphous solids.
Q.9. What is isotropy?
Ans. The phenomenon due to which in amorphous solids a physical property has same value in all the direction is called isotropy.
Q.10. What is anisotropy?
Ans. The phenomenon due to which in crystalline solids same physical properties have different values in different directions is called anisotropy.
Q.11. Which type.of solids have sharp melting point?
Ans. Crystalline solids have sharp melting point.
Q.12. Which type of solids have definite enthalpy of fusion?
Ans. Crystalline solids have definite enthalpy of fusion.
Q.13. Which type of solids have long range ordered arrangement of constituent particles?
Ans. Crystalline solids have long range order.
Q.14 What is photovoltaic materials? Give example.
Ans. A substance which converts solar energy into electrical energy is called photovoltaic materials e.g. amorphous silicon.
Q.15. Which type of intermolecular force is present in non-polar molecular solids?
Ans. London dispersion force is present in non polar molecular solids.
Q.16. Which type of intermolecular force is present in polar molecular solids?
Ans. Dipole-dipole interaction and H-bonding is present in polar molecular solids.
Q.17. Which type of intermolecular force is present in ice?
Ans. H-bonding is present in ice.
Q.18. Which type of solids are hard and brittle?
Ans. Ionic solids are hard and brittle.
Q.19. Which type of solids are soft and brittle?
Ans. Molecular solids are soft and brittle.
Q.20. Which type of solids are called giant molecules?
Ans. Covalent (network) solids are called giant molecules.
Q.21. Which type of motion is possible in solid particles?
Ans. Only oscillatory motion is possible in solid particles.
Q.22. Which property of glass enables it to be moulded and blown into various shapes?
Ans. Amorphous solids soften over a range of temperature. This enables the glass to be moulded and blown into various shapes.
Q.21. What is a unit cell?
Ans. The smallest repeating pattern of constituent particles which represents structure of a solid is called unit cell.
Q.22. Define space lattice.
Ans. The arrangement of lattice points in three dimensional space of a solid is called space lattice.
Q.23. What are primitive and non-primitive unit cells?
Ans. A unit cell in which lattice points are only at the comers are called primitive unit cells. A unit cell in which lattice points are at the corners as well as at the centres of body, faces, edges etc. are called non- primitive unit cells.
Q.24. What is the co-ordination number of each lattice point in hexagonal close pack structure?
Ans. 12 (6 in the same layer + 3 each above and below layer).
Q.25. What is the co-ordination number in the body centred cubic close packed structure?
Q.26. What is the co-ordination number in the cubic close packed (face centred-cubic) structure?
Q.27. Which type of voids are present in a solid crystal?
Ans. Two types of voids present in a solid crystals are (a) tetrahedral and (b) octahedral.
Q.28. What is the coordination number of octahedral voids?
Q.27. What is the number of octahedral and tetrahedral voids per unit cell of cubic close packing (fee)?
Ans. Number of tetrahedral voids = 8, number of octahedral voids = 4.
Q.28. What happens to a sodium chloride structure when high pressure is applied to it?
Ans. When presence is applied and structure (coordination number =6:6) changes to CsCI structure (coordination number =8:8).
Q.29. What happens to a caesium chloride structure when high temperature is applied to it?
Ans. When high temperature is applied CsCI structure (coordination number =8:8) changes to and structure (coordination number =6:6).
Q.30. What is the name of unit cell in which atoms are placed at the corners of all 12 edges of a cubic unit cell?
Ans. Simple cubic (or primitive)
Q.31. Silver halide forms crystals similar to NaCl. Under what condition these changes to CsCI crystals?
Ans. When high pressure is applied and type structure changes to CsCI type structure.
Q.32. Name the type of structure of CsCI.
Ans. Body centred cubic (bcc).
Q.33. What do you mean by imperfections in solid?
Ans. Any type of deviation in regular arrangement of crystalline solid is called imperfections in solid.
Q.34. What is point defect?
Ans. Deviation from ideal arrangement around a point in a crystalline solid is called point defect.
Q.35. What is Frenkel defect?
Ans. The defect in which an ion is dislocated from its normal site to an interstitial site is called Frenkel defect.
Q.36. What is Schottky defect?
Ans. The defect in which cations and anions are missing from their lattice sites in the ratio of its normal formula is called Schottky defect.
Q.37. Which point defect lowers density of solid?
Ans. Schottky defect lowers density of solid.
Q.38. What type of compounds exhibit Schottky defect?
Ans. Schottky defect is shown by ionic substances in which the cation and anion are almost same in size.
Q.39. What is the effect on the density of a crystal due to Schottky defect?
Ans. Density of solid decreases due to Schottky defect.
Q.40. Name a compound in which Frenkel and Schottky defect are present together.
Ans. In AgBr both Frenkel and Schottky defect are present.
Q.41. Why is the Frenkel defect not found in pure alkali metal halides?
Ans. Alkali metal halides have similar size of cations and anions.
Q.42. Zinc oxide is white but becomes yellow-on heating. Why?
Ans. Zinc oxide on heating becomes yellow due to metal excess defect causes by the loss of oxide ions.
Q.43. NaCl crystals when heated in sodium vapours become yeltew Why?
Ans. NaCI crystals when heated in sodium vapour becomes yellow due to metal excess defect caused by addition of Na metal. KCl crystals when heated in potassium vapours become violet due to metal excess defect caused by addition of K atom.
Q.44. KCl crystals when heated in potassium vapours become violet Why?
Ans. The anionic sites occupied by unpaired electrons in a solid having metal excess defect are called F centres.
Q.45. What are F centres?
Ans. In Frenkel defect total ions in a solid remain same hence density of solid remains same.
Q.46. Why there is no change in density of a solid due to Frenkel defect?
Ans. Presence of F centres causes colour.
Q.47. Name a salt that can be added to AgCl so as to produce cation vacancy.
Ans. A substance which remain magnetized in absence of magnetic field is called ferromagnetic substance,
Example: Fe, Co, Ni, etc.
Q.48. What are ferromagnetic substances?
Ans. Addition of an appropriate amount of suitable impurity in a crystalline solid is called doping. Doping is done to increasing conductivity of intrinsic semiconductors.
Q.49. What is doping? Why is it done?
Ans. Phosphorus doped silicon is n-type semiconductor whereas gallium doped silicon is a p-type semiconductor.
Q.50. What may be the difference between phosphorus doped and gallium doped semiconductors.
Ans. Pure silicon is an insulator but it behaves as semiconductor on heating because with increase in temperature movement of holes as well as electrons becomes faster.