The Solid State (Questions)

          A.      Very Short – Answer Questions

1.          What is crystalline solid?

2.          What is an amorphous solid?

3.          Name any five amorphous solids.

4.          Name any five crystalline solids.

5.          What is anisotropy?

6.          Why are crystals anisotropic?

7.          Under which situations can an amorphous substance change to crystalline form?

8.          What are different types of crystalline solids?

9.          What are the characteristics of a molecular solid?

10.      Why are liquids and gases categorised as fluids?

11.      Why are solids incompressible?

12.      What is coordination numbers?

13.      What is a unit cell?

14.      What is primitive lattices?

15.      What are centred lattices?

16.      An element A adopts a body-centred cubic structure. How many atom does the atom at the body-centre touch? What about the atom at the corner?

17.      What is packing fraction?

18.      A large number ,N, of circular discs of negligible thickness are arranged in a plane in 
        (i) square packing, and               (ii)hexagonal packing 
        What is the total number of holes in (i) and (ii)? Calculate the packing fraction in each case.

19.      How many tetrahedral and octahedral holes are present in a FCC unit cell?

20.      What is a point defect?

21.      What is a Schottky defect?

22.      What is Frenkel defact?

23.      What is an F-centre?

24.      Why does table salt, NaCl, sometimes appear yellow in colour?

25.      Why is FeO (s) not formed in stoichiometric composition?

26.      How do the energy band diagrams of metals, insulator and semiconductor differ?

27.      How does temperature affect the conductivity of metals, insulators and semiconductors?

28.      What is doping?

29.      What element should Ge be doped with to get 
        (i) an n-type semiconductor, and                (ii) a p-type semiconductor?

30.      Explain why does conductivity of germanium crystals increase on doping with galium.

            B.      Short-Answer Questions

1.      How solids are different from liquids and gases?

2.      Why does the rapid cooling of molten material result in formation of amorphous material?

3.      Why is diamond hard and graphite soft, though both are network covalent solids?

4.      Graphite is expected to conduct electricity in directions parallel to its sheet, but it conducts in all directions. Why does this happen?

5.      Ionic compounds do not conduct electricity in the solid state but do so on melting or in aqueous solution. Explain.

6.      Which type of solid has highest melting point?

7.      With reference to 3-d lattices, how many unit cells are the following points common to?

(i)Corner                             (ii)Face-centre

(iii)Body-centre                (iv)Edge-centre

8.      With reference to a cubic unit of cell of edge-length a, what are the distances between

(i) The corner points on a face diagonal,

(ii) The corner points on a body diagonal,

(iii) The face-centre points on perpendicular faces,

(iv) The face-centre points on parallel faces,

(v) A corner point and the nearest face-centre point,and

(vi) A corner point and the body centre?

9.      What is the maximum separation between the lattice points in a (i) primitive cubic unit cell, (ii)body-centred cubic unit cell, and (iii) face-centred cubic unit cell?

10.  What are HCP and CCP? Which of these has a higher packing of spheres?

11.  What are tetrahedral and octahedral holes in the closest packing of spheres?

12.  Why does the structure of CsCI differ from that of NaCI?

13.  Why defects are present in crystal structures at ordinary temperatures and why do they increase with rise in temperature?

14.  Why is a cation Frenkel defect more common than an anion Frenkel defect?

15.  Anionic Frenkel defect is found in ionic solids with a fluorite structure. Why is this so?

16.  Why does ZnO turn yellow on heating and become white again on cooling?

17.  What is a nonstoichiometric defect? Give an example.

18.  What are valence and conduction bands?

19.  Explain the electrical conductivity of metals in terms of the band theory.

20.  Semiconductor are insulator at 0 K. How do they become weakly conducting as temperature increases?

21.  What is the difference between intrinsic and extrinsic semiconductors?

22.  What are n-type and p-type semiconductors?

23.  What are the different types of magnetic substances?

24.  How does a diamagnetic substance differ from a paramagnetic substance?

25.  Describe the different types of magnetic behavior shown by solids.