(1 - MARK QUESTIONS)
1. What are anistropic substances?
2. Why are amorphous solids isotropic in nature?
3. Why glass is regarded as an amorphous solid?
4. Define the term 'crystal lattice.’
5. Define the term voids.
6. What type of stochiometric defect is shown by (i) ZnS and (ii) CsCl?
7. If the formula of a compound is A2B, which sites would be occupied by A ions?
8. What is the coordination number for
(a) an octahedral void
(b) a tetrahedral void.
9. How many octahedral voids are there in 1 mole of a compound having cubic closed packed structure?
10. Arrange simple cubic, bcc and fcc lattice in decreasing order of the fraction of the unoccupied space.
11. How much space is empty in a hexagonal closed packed solid?
12. An element crystallises separately both in hcp and ccp structure. Will the two structures have the same density? Justify your answer.
13. In NaCl crystal, Cl– ions form the cubic close packing. What sites are occupied by Na+ ions.
14. In Corundum, O2– ions from hcp and Al3+ occupy two third of octahedral voids. Determine the formula of corundum.
15. Why is Frenkel defect not found in pure alkali metal halides?
16. Which point defect is observed in a crystal when a vacancy is created by an atom missing from a lattice site.
17. Define the term ‘doping’.
18. Why does conductivity of silicon increase with the rise in temperature.
19. Name the crystal defect which lowers the density of an ionic crystal.
20. What makes the crystal of KCl sometimes appear violet?
21. Which point defect in ionic crystal does not alter the density of the relevant solid?
22. Name one solid in which both Frenkel and Schottky defects occur.
23. Which type of defects are known as thermodynamic defects?
24. In a p-type semiconductor the current is said to move through holes.Explain.
25. Solid A is very hard, electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it?