Topper's Academy

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TOPPER'S ACADEMY
CHAPTER 1
VSA QUESTIONS (1 MARK)
1. What are Bravais lattices?
2. Why are amorphous solids isotropic in nature?
3. Why glass is regarded as an amorphous solid?
4. Define the term 'crystal lattice.’
5. Name the crystal system for which all four types of unit cells are possible. [Ans. Orthorhombic]
6. What is the total number of atoms per unit cell in a fcc crystal structure? [Ans. 4]
7. What difference in behaviour between the glass and sodium chloride would you expect to observe,
if you break off a piece of either cube?
8. Define the term voids.
9. What type of stochiometric defect is shown by (i) ZnS and (ii) CsCl?
[Hint. : (i) Frenkel defect (ii) Schottky defect]
*10. If the formula of a compound is A2B, which sites would be occupied by A ions?
[Hint. : Number of A atoms is double to B, so it occupied tetrahedral void]
11. What is the coordination number for
(a) an octahedral void
(b) a tetrahedral void.
[Hint. : (a) 6; (b) 4 ]
*12. How many octahedral voids are there in 1 mole of a compound having cubic closed packed
structure? [Ans. : 1 mole]
13. What does the term ‘Coordination number’ indicate?
14. Arrange simple cubic, bcc and fcc lattice in decreasing order of the fraction of the occupied space.
15. How much space is empty in a hexagonal closed packed solid?
16. An element crystallises separately both in hcp and ccp structure. Will the two structures have the
same density? Justify your answer.
*17. Write dimensions and bond angles of match-box type of unit cells.
*18. Calculate the number of atoms in a cubic unit cell having one atom on each corner and two atoms
on each body diagonal.
19. In NaCl crystal, Cl– ions form the cubic close packing. What sites are occupied by Na+ ions.
20. In Corundum, O2– ions from hcp and Al3+ occupy two third of octahedral voids. Determine the
formula of corundum.
21. Why is Frenkel defect not found in pure alkali metal halides?
22. Which point defect is observed in a crystal when a vacancy is created by an atom missing from
a lattice site.
23. Define the term ‘doping’.
24. Although pure silicon is an insulator then how does it behave as a semiconductor on heating.
25. Name the crystal defect which lowers the density of an ionic crystal.
26. What makes the crystal of KCl sometimes appear violet?
27. Which Point defect in ionic crystal does not alter the density of the relevant solid?
28. Name one solid in which both Frenkel and Schottky defects occur.
29. Fe3O4 is ferrimagnetic at room temperature but becomes paramagnetic at 850 K. Why?
30. Which type of defects are known as thermodynamic defects?
31. In a p-type semiconductor the current is said to move through holes. Explain.
32. 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?

SA (I) TYPE QUESTIONS (2 MARKS)
1. List four distinctions between crystalline and amorphous solids with one example of each.
2. Give suitable reason for, the following–
(a) Ionic solids are hard and brittle
(b) Copper is malleable and ductile
3. Define F–centres. Mention its two consequences.
4. What is packing efficiency. Calculate the packing efficiency in body centered cubic structure.
5. Explain :
(a) List two differences between metallic and ionic crystals.
(b) Sodium chloride is hard but sodium metal is soft.
6. Account for the following :
(a) Glass objects from ancient civilizations are found to becomes milky in appearances.
(b) Window glass panes of old buildings are thicker at the bottom than at the top.
7. Why graphite is soft lubricant and good conductor of electricity?
8. Explain the term “Unit Cell”. Name the parameters that characterize a unit cell.
*9. What do you understand by the following types of stacking sequences :
(a) AB AB ............... (b) A B CABC .................
What kind of lattices do these sequences lead to?
10. How can you calculate the density of a crystal whose length of the edge of the unit cell is known?
11. Explain how much portion of an atom located at (a) corner (b) body centre (c) face-centre and
(d) edge centre of a cubic unit cell, is part of its neighbouring unit cells.
*12. In a fcc arrangement of A and B atoms. A are present at the corners of the unit cell and B are
present at the face centres. If one atom of A is missing from its position at the corners, what is
the formula of the compound? [Ans. : A7B24]
*13. A compound made up of elements ‘A’ and ‘B’ crystallises in a cubic close packed structure. Atom
A are present on the corners as well as face centres, whereas atoms B are present on the edgecentres
as well as body centre. What is the formula of the compound? [Ans. A4B4 or AB]
14. Explain the terms :
(a) Intrinsic semiconductors
(b) Extrinsic semiconductor.
15. Pure silicon is an insulator. Silicon doped with phosphorus is a semiconductor. Silicon doper with
gallium is also a semiconductor. What is the difference between the two types?
16. Explain how vacancies are introduced in a solid NaCl crystal when a compound containing cation
of higher valence is added to it.
17. What is meant by non-stoichiometric defect? Ionic solids which have anionic vacancies due to
metal excess defect develop colour. Explain with the help of suitable example.
18. Define the term ‘point defects’ Mention are main difference between stoichiometric and nonstoichiometric point defects.
SA (II) TYPE QUESTIONS (3 MARKS)
1. Write the relationship between atomic radius (r) and edge length (a) of cubic unit cell for
(a) Simple cubic unit cell
(b) Body centred cubic unit cell
(c) Face centred cubic unit cell
2. Write and explain three differences between Schottky and Frenkel defects under the heads :
(i) Effect on density
(ii) Effect on electrical conductivity
(iii) Effect on stability of the crystal
3. What is a semiconductor? Describe the two main types of semiconductors on the basis of their
conductance mechanism.
4. Explain the following with one examples each :
(a) Ferrimagnetism (b) Anti ferromagnetism
(c) 13-15 compounds
5 (a) Name of defect present in ionic solid.
(b) Out of AgCl and NaCl, which is most likely to show this type of defect and why?
(c) Why this defect is also known as dislocation defect?

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