The Solid State – Class 12 Chemistry Notes | CBSE NCERT Based

 📚 Chapter: The Solid State – Class 12 Chemistry Notes



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🔸 Introduction to Solid State


Solids have definite shape, volume, and are incompressible.


Intermolecular forces are strongest in solids.


Two main types:


1. Crystalline Solids



2. Amorphous Solids






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🔹 1. Classification of Solids


Type Properties Example


Crystalline Ordered, definite melting point NaCl, Quartz

Amorphous Irregular, softens over a range of temp. Glass, Plastic




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🔹 2. Crystal Lattices and Unit Cell


Crystal lattice: 3D arrangement of points representing atoms.


Unit cell: Smallest repeating unit in crystal lattice.


Types of Unit Cells:


Primitive: Atoms only at corners


Body-centered (BCC): One atom at center


Face-centered (FCC): One atom at each face





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🔹 3. Number of Atoms in Unit Cell


Type of Unit Cell Formula to Calculate Atoms Total Atoms


Simple Cubic 8 corners × 1/8 1

BCC 8 corners × 1/8 + 1 center 2

FCC 8 corners × 1/8 + 6 faces × 1/2 4




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🔹 4. Packing Efficiency


Simple Cubic: 52.4%


BCC: 68%


FCC / CCP: 74% (highest)




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🔹 5. Voids


Void = empty space in packing


Closer packing = less voids


FCC has least voids




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🔹 6. Types of Crystals Based on Bonding


Type Bond Type Examples


Ionic Electrostatic NaCl, KCl

Covalent (Network) Covalent Bonds Diamond, SiO₂

Molecular van der Waals/H-bond Ice, CO₂

Metallic Metallic bonding Cu, Fe




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🔹 7. Imperfections in Solids


Point Defects:


Vacancy defect: Missing atom


Interstitial defect: Extra atom in void



Stoichiometric vs Non-Stoichiometric Defects


Schottky & Frenkel = Stoichiometric





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🔹 8. Electrical and Magnetic Properties


Conductor: Free electrons (e.g. Cu)


Insulator: No conduction (e.g. glass)


Semiconductors: Small gap (e.g. Si, Ge)



Magnetic Types:


Diamagnetic: Weakly repelled


Paramagnetic: Weakly attracted


Ferromagnetic: Strong attraction




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📌 Conclusion:


Solid State chapter builds base for physical properties of matt

er in Chemistry. Diagrams like unit cells and packing structures make it easier to understand.



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✍️ Written by: Shahid – Study with Shahid


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