TYPES OF SOLIDS Two types based upon atomic

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

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: Na. Cl, Cs. Cl, etc.

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 supercooled liquids. � No sharp m. p. � Isotropic. � No definite geometrical shape. � Do not give x-ray diffraction bands. � Examples: glass, rubber, plastics.

Types of crystal structures � Ionic crystals � Covalent crystals � Molecular crystals � Metallic crystals

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: Ø AB types. Ø AB 2 types.

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.

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.

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.