TYPES OF SOLIDSTwo types (based upon atomic arrangement, bindingenergy, physical & chemical properties):1. Crystalline2. Amorphous
Crystalline solids The building constituents arrange themselves in regularmanner throughout the entire three dimensional network. Existence of crystalline lattice. A crystalline lattice is a solid figure which has a definitegeometrical 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.
AMORPHOUS SOLIDS Derived from Greek word ‘Omorphe’ meaningshapeless. No regular but haphazard arrangement of atoms ormolecules. 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.
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 inmolten 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.
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 ionssurrounded 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 overthe entire crystal. High density.