1. Define the term 'amorphous'. Give a few examples of amorphous solids.     

Irregular shape Gradually soften over a range of temperature When cut with a sharp edged tool, they cut into two pieces with irregular surfaces. They do not have definite enthalpy of fusion. Example : glass , rubber and plastics  

2. What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?                

Glass is a supercooled liquid and amorphous substances. Quartz is a crystalline form of silica in which tetrahedral units of of SiO4 are linked with each other in such a way that the oxygen atom of one tetrahedron is shared with another Si atom. Quartz can converted into silica by melting it and cooling it very rapidly. In glass sio4 atoms are joined in a random manner. 

3. classify each of the following solids as ionic, metallic, molecular, (covalent) or amorphous.  

1 Tetra phosphorus decoxide (P4O10) 


3. Ammonium phosphate (NH4)3PO4 

4.  Brass 

5. SiC 

6.  Rb 

7. I2 

8.  LiBr 

9. P4 

10.  Si 

11.  Plastic 


(NH4)3PO4 and



Brass and Rb


P4 O10, I2,P4


Graphite, SiC, Si



4. (i) What is meant by the term 'coordination number'? 

(ii) What is the coordination number of atoms: 

(a) in a cubic close-packed structure? 

(b) in a body-centred cubic structure?  

1. The number of nearest neighbours of a particle is called as a coordination number. 

2. a. 12     


5. How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell? Explain 

6. 'Stability of a crystal is reflected in the magnitude of its melting points'. Comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules? 

• Higher the melting point , greater the force of holding the constituent particles together, and this greater stability of Crystal. Melting point of water 273 K, ethyl alcohol 150 5.7 K, di ethyl ether  156.8K, methane 90.5 K. 
• The intermolecular forces present in case of water and ethyl alcohol is mainly due to the presence of hydrogen bonding which is responsible for the higher melting points. Hydrogen bond is stronger in case of water than ethyl alcohol. Hence water has higher melting point than ethyl alcohol. Dipole dipole interaction is present in case of diethyl Ether. The meeting has weak Vander Waal forces. 

7. How will you distinguish between the following pairs of terms: 
(i) Hexagonal close-packing and cubic close-packing?  
(ii) Crystal lattice and unit cell? 
(iii) Tetrahedral void and octahedral void? 

(i)Hexagonal close packing - The spheres third layer are vertically above the spheres of first layer  ( ABABAB) type.on the other hand cubic close packing, the spheres of fourth layer are present above the first layer. 

(ii) crystal lattice  - it  depicts  actual shape as well as size  of constituent particle in the crystal. So it is called is a space lattice Each bricks represent the unit cell while the block is similar to space . Does the unit cell is fundamental building block of space lattice. 

• Tetrahedral voids – triangular voids is formed when  triangular void is made by three spheres of particular layer and touching each other. Octahedral void is formed by when three spheres are arranged at the corners of equatorial triangle are placed over another set of spheres. 

8. How many lattice points are there in one unit cell of each of the following lattice? 
(i) Face-centered cubic 
(ii) Face-centered tetragonal 
(iii) Body-centered   
(i) Face centered tetragonal 
(ii) Lattice points is body centered  Unit cell = 4 
(iii) 8 (at the corners)+ 1 ( corners)= 9 
Unit cell = 29.  

9. Explain 
(i) The basis of similarities and differences between metallic and ionic crystals. 
(ii) Ionic solids are hard and brittle   



• There is a electrostatic force of attraction between ionic and metallic crystals 
• Both have high melting points 
• In both cases bonds are non directional   

• Ionic bonds are bad conductor of electricity in solid state and metallic conductors are good conductors of electricity in solid state.  
• Ionic crystals are strong due to strong electrostatic force of interaction and metallic crystals are weak  depend upon number of valence electron and size of kernel. 

(ii) Ionic solids are hard and brittle    
Ionic solids are hard due to high electrostatic force of attraction. The brittleness of ionic crystals due to them non directional  bonds in them.  

10. Calculate the efficiency of packing in case of a metal crystal for

(i) simple cubic 

(ii) body-centred cubic 

(iii) face-centred cubic (with the assumptions that atoms are touching each other).


11. Silver crystallises in fcc lattice. If edge length of the cell is 4.07 × 10–8 cm and density is 10.5 g cm–3, calculate the atomic mass of silver? 

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