Solid State Class 12 Chemistry Maharashtra Board Textbook Solution

1. Choose the most correct answer.

i. Molecular solids are
a. crystalline solids
b. amorphous solids
c. ionic solids
d. metallic solids

ii. Which of the follwong is n-type semiconductor?
a. Pure Si
b. Si doped with As
c. Si doped with Ga
d. Ge doped with In

iii. In Frenkel defect
a. electrical neutrality of the substance is changed.
b. density of the substance is changed.
c. both cation and anion are missing
d. overall electical neutrality is preserved.

iv. In crystal lattice formed by bcc unit cell the void volume is
a. 68 % 

b. 74 %
c.32 %

d. 26 %

v. The coordination number of atoms in bcc crystal lattice is
a. 2

b. 4

c. 6

d. 8

vi. Which of the following is not correct?
a. Four spheres are involved in the formation of tetrahedral void.
b. The centres of spheres in octahedral voids are at the apices of a regular tetrahedron.
c. If the number of atoms is N the number of octahedral voids is 2N.
d. If the number of atoms is N/2, the number of tetrahedral voids is N.

vii. A compound forms hcp structure. Number of octahedral and tetrhedral voids in 0.5 mole of substance is respectively
a. 3.011×1023, 6.022×1023

b. 6.022×1023, 3.011×1023

c. 4.011×1023, 2.011×1023

d. 6.011×1023, 12.022×1023

vii. Pb has fcc structure with edge length of unit cell 495 pm. Radius of Pb atom is
a. 205 pm

b. 185 pm

c. 260 pm

d. 175 pm

2. Answer the following in one or two sentences

i. What are the types of particles in each of the four main classes of crystalline solids ?

ii. Which of the three types of packing used by metals makes the most efficient use of space and which makes the least efficient use?

iii. The following pictures show population of bands for materials having different electrical properties.
Classify them as insulator, semiconductor or a metal.

picture of metal insulator and semiconductor

iv. What is the unit cell?

v. How does electrical conductivity of a semiconductor change with temperature? Why?

vi. The picture represents bands of MOs for Si. Label valence band, conduction band and band gap.

metallic orbital of silicon

vii. A solid is hard, brittle and electrically nonconductor. Its melt conducts electricity. What type of solid is it?

viii. Mention two properties that are common to both hcp and ccp lattices.

ix. Sketch a tetrahedral void.

x. What are ferromagnetic substances?

3. Answer the following in brief.

i. What are valence band and conduction band?

ii. Distinguish between ionic solids and molecular solids.

iii. Calculate the number of atoms in fcc unit cell.

iv. How are the spheres arranged in first layer of simple cubic close-packed structures? How are the successive layers of spheres placed above this layer?

v. Calculate the packing efficiency of metal crystal that has simple cubic structure.

vi. What are paramagnetic substances? Give examples.

vii. What are the consequences of Schottky defect?

viii. Cesium chloride crystallizes in cubic unit cell with Cl ions at the corners and a Cs⊕ ion in the centre of the cube. How many CsCl molecules are there in the unit cell?

ix. Cu crystallizes in fcc unit cell with edge length of 495 pm. What is the radius of Cu atom?

x. Obtain the relationship between density of a substance and the edge length of unit cell.

4. The density of iridium is 22.4 g/cm3. The unit cell of iridium is fcc. Calculate the
radius of iridium atom. Molar mass of iridium is 192.2 g/mol. (136 pm)

5. Aluminium crystallizes in cubic close packed structure with unit cell edge length of 353.6 pm. What is the radius of Al atom? How many unit cells are there in 1.00 cm3 of Al? (125 pm, 2.26×1022)

6. In an ionic crystalline solid atoms of element Y form hcp lattice. The atoms of element X occupy one third of tetrahedral voids. What is the formula of the compound ? 

7. How are tetrahedral and octahedral voids formed?

8. Third layer of spheres is added to second layer so as to form hcp or ccp structure. What is the difference between the addition of third layer to form these hexagonal close-packed structures?

9. An element with molar mass 27 g/mol forms cubic unit cell with edge length of 405 pm. If density of the element is 2.7 g/cm3. What is the nature of cubic unit cell? (fcc or ccp)

10. An element has a bcc structure with unit cell edge length of 288 pm. How any unit cells and number of atoms are present in 200 g of the element?

11. Distinguish with the help of diagrams metal conductors, insulators and semiconductors from each other

12. What are n-type semiconductors? Why is the conductivity of doped n-type semiconductor higher than that of pure semiconductor? Explain with diagram.

13. Explain with diagram, Frenkel defect. What are the conditions for its formation? What is its effect on density and electrical neutrality of the crystal?

14. What is an impurity defect? What are its types? Explain the formation of vacancies through aliovalent impurity with example.