Class 12th "SOLID STATE"

CRYSTALS/CRYSTALLINE

A constituents are arranged A highly ordered microscopic structure,forming a crystal lattice that extend in all directions. 

               Fig. 1 : Crystal

CLASSIFICATION OF CRYSTALS : These are four types of crystals are following : 

1. Ionic Crystals : It is binding by ionic        bonds.

             Fig. 2 : (NaCl) 

Properties/characteristics of Ionic Crystals : 

• It is hard and brittle. 

• High melting point. 

• High heat of fusion. 

• Poor thermal and electric                      conductors. 

Example : NaCl, PbS. etc. 

2. Molecular Crystals :  It is binding            by Vander waal's forces ( London dispersion, dipole-dipole force, hydrogen bonds). 

            Fig. 3 : (Ice) 

Properties of Molecular Crystals : 

• Low to moderately high melting          points. 

• Poor conductors of electricity. 

Example : Ice, dry ice etc. 

3. Covalent Crystals : It is binded by covalent bonds. 

            Fig. 4 : Diamond & Graphite

Properties of Covalent Crystals : 

• Very hard. 

• High melting points. 

• Poor thermal and electric conductors. 

Example : Diamond, Quartz, Graphite (exception) etc. 

4. Metallic Crystals : It is binding by metallic bonds. 

                      Fig. 5

Properties of Metallic Crystals : 

• Soft to very hard. 

• Low to very high melting points. 

• Excellent thermal and electrical conductors. 

Example : All metallic elements like Fe, Cu, Zn, Si, Ag, Au etc. 

CRYSTAL LATTICE

A regular three dimentional arrangement of point in space is called Crystal lattice. 

                       Fig. 6 

    

       

                   THANK YOU !