Solids

Solids: State of matter with definite shape and volume. Atoms/ions/molecules are closely packed and held by strong cohesive forces.

Types:
1. Crystalline Solids: Regular 3D arrangement (Long-range order). Sharp Melting Points. Anisotropic. Example: NaCl.
2. Amorphous Solids: Irregular arrangement (No long-range order). Melt over a range. Isotropic. Example: Glass, Rubber, Plastics.

Geometrical Shape: Definite faces and angles.
Symmetry: Elements of symmetry (plane, axis, center).
Cleavage Planes: Break along definite planes.
Anisotropy: Variation of physical properties with direction (e.g., Conductivity in Graphite).
Isomorphism: Different compounds having same crystal structure (e.g., NaNO₃ and CaCO₃).
Polymorphism: Single substance existing in multiple crystalline forms (e.g., Carbon has Diamond, Graphite).

Crystal Lattice: An array of points representing atoms/ions/molecules in a 3D space.
Unit Cell: The smallest repeating unit which generates the entire crystal lattice.
Parameters: 3 edges (a, b, c) and 3 angles (α, β, γ).

• Cubic: a=b=c, α=β=γ=90° (e.g., NaCl, Diamond).
• Tetragonal: a=b≠c, α=β=γ=90° (e.g., SnO₂).
• Orthorhombic: a≠b≠c, α=β=γ=90° (e.g., Rhombic Sulphur).
• Monoclinic: a≠b≠c, α=γ=90°, β≠90° (e.g., Sugar, Monoclinic Sulphur).
• Hexagonal: a=b≠c, α=β=90°, γ=120° (e.g., Graphite, Ice).
• Rhombohedral (Trigonal): a=b=c, α=β=γ≠90° (e.g., NaNO₃).
• Triclinic: a≠b≠c, α≠β≠γ≠90° (e.g., CuSO₄.5H₂O).

1. Ionic Solids: Introduction of oppositely charged ions held by Electrostatic forces. High M.P., Brittle, Non-conductors in solid (Conductors in molten/aqueous). Example: NaCl. Lattice Energy: Energy released when ions form crystal (U ∝ Q⁺Q^-/r).

2. Covalent Solids: Network of atoms held by covalent bonds. Very hard, High M.P. Example: Diamond (sp³, insulator), Graphite (sp², conductor).

3. Molecular Solids: Molecules held by weak Van der Waals forces. Volatile, Low M.P. soft. Example: Ice, Dry Ice (Solid CO₂), Iodine.

4. Metallic Solids: Metal cations in a sea of delocalized electrons. Ductile, Malleable, Good conductors. Example: Cu, Fe, Al.