Class 12 Chemistry - Chapter 1: The Solid State
1. General Characteristics of Solid State
Solids have definite mass, volume, and shape. They are rigid and incompressible. The
intermolecular distances are short and intermolecular forces are strong. Particles in solids have fixed
positions and can only oscillate about their mean positions. Types: Crystalline and Amorphous.
2. Classification of Solids
(a) Crystalline Solids - Have long-range order and sharp melting points. E.g., NaCl, Quartz.
(b) Amorphous Solids - Irregular arrangement, soften over a range. E.g., Glass, Plastic.
Types of Crystalline Solids:
- Ionic Solids: Strong electrostatic forces, e.g., NaCl.
- Molecular Solids: Held by van der Waals forces/H-bonding. E.g., Ice.
- Covalent/Network Solids: Extensive covalent bonding. E.g., Diamond, SiO2.
- Metallic Solids: Positive ions in electron cloud. Conduct electricity.
3. Crystal Lattices and Unit Cells
- A crystal lattice is a 3D arrangement of points.
- Unit cell: Smallest repeating unit with entire crystal structure.
- Parameters: Edge lengths (a, b, c) and angles (alpha, beta, gamma).
- Types: Primitive (simple), Body-Centred (BCC), Face-Centred (FCC), End-Centred.
4. Packing in Solids
- Close packing increases efficiency.
- Types: Hexagonal Close Packing (HCP), Cubic Close Packing (CCP/FCC), Body-Centred Packing.
- Packing Efficiency: % of volume occupied by particles.
- For FCC/CCP: 74%, BCC: 68%, Simple Cubic: 52%.
5. Density of Unit Cell
Formula: Density (rho) = (Z x M) / (a^3 x NA)
1. General Characteristics of Solid State
Solids have definite mass, volume, and shape. They are rigid and incompressible. The
intermolecular distances are short and intermolecular forces are strong. Particles in solids have fixed
positions and can only oscillate about their mean positions. Types: Crystalline and Amorphous.
2. Classification of Solids
(a) Crystalline Solids - Have long-range order and sharp melting points. E.g., NaCl, Quartz.
(b) Amorphous Solids - Irregular arrangement, soften over a range. E.g., Glass, Plastic.
Types of Crystalline Solids:
- Ionic Solids: Strong electrostatic forces, e.g., NaCl.
- Molecular Solids: Held by van der Waals forces/H-bonding. E.g., Ice.
- Covalent/Network Solids: Extensive covalent bonding. E.g., Diamond, SiO2.
- Metallic Solids: Positive ions in electron cloud. Conduct electricity.
3. Crystal Lattices and Unit Cells
- A crystal lattice is a 3D arrangement of points.
- Unit cell: Smallest repeating unit with entire crystal structure.
- Parameters: Edge lengths (a, b, c) and angles (alpha, beta, gamma).
- Types: Primitive (simple), Body-Centred (BCC), Face-Centred (FCC), End-Centred.
4. Packing in Solids
- Close packing increases efficiency.
- Types: Hexagonal Close Packing (HCP), Cubic Close Packing (CCP/FCC), Body-Centred Packing.
- Packing Efficiency: % of volume occupied by particles.
- For FCC/CCP: 74%, BCC: 68%, Simple Cubic: 52%.
5. Density of Unit Cell
Formula: Density (rho) = (Z x M) / (a^3 x NA)
