1. TYPES OF SOLIDS
Two types (based upon atomic arrangement, binding
energy, physical & chemical properties):
1. Crystalline
2. Amorphous

2. Crystalline solids
 The building constituents arrange themselves in regular
manner throughout the entire three dimensional network.
 Existence of crystalline lattice.
 A crystalline lattice is a solid figure which has a definite
geometrical shape, with flat faces and sharp edges.
 Incompressible orderly arranged units.
 Definite sharp melting point.
 Anisotropy.
 Definite geometry.
 Give x-ray diffraction bands.
 Examples: NaCl, CsCl, etc.

3. AMORPHOUS SOLIDS
 Derived from Greek word ‘Omorphe’ meaning
shapeless.
 No regular but haphazard arrangement of atoms or
molecules.
 Also considered as non-crystalline solids or super-
cooled liquids.
 No sharp m.p.
 Isotropic.
 No definite geometrical shape.
 Do not give x-ray diffraction bands.
 Examples: glass, rubber, plastics.

4. Types of crystal structures
 Ionic crystals
 Covalent crystals
 Molecular crystals
 Metallic crystals

5. Ionic crystals
 Lattice points are occupied by positive and negative ions.
 Hard and brittle solids.
 High m.p due to very strong electrostatic forces of attraction.
 Poor conductors of electricity in solid state but good in
molten state.
 Packing of spheres depends upon:
a) presence of charged species present.
b) difference in the size of anions and cations.
 Two types:
 AB types.
 AB2 types.

6. Covalent crystals
 Lattice points are occupied by neutral atoms.
 Atoms are held together by covalent bonds
 Hard solids.
 High m.p.
 Poor conductors of electricity.
 Two common examples: diamond & graphite.

7. Molecular crystals
 Lattice points are occupied by neutral molecules.
 The molecules are held together by Vander Waal’s forces.
 Very soft solids.
 Low m.p.
 Poor conductors of electricity.

8. Metallic crystals
 Lattice points are occupied by positive metal ions
surrounded by a sea of mobile e-.
 Soft to very hard.
 Metals have high tensile strength.
 Good conductors of electricity.
 Malleable and ductile.
 Bonding electrons in metals remain delocalized over
the entire crystal.
 High density.