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Class 12 ChemistryChapter Notes
1 chapters · Definitions, key points, formulas & exam tips
Ch 1
The Solid State
Key Definitions
Unit Cell: The smallest repeating unit of a crystal lattice.
Coordination Number: Number of nearest neighbours of a particle in a crystal.
Packing Efficiency: Percentage of crystal volume occupied by constituent particles.
Key Points to Remember
- →Types of solids: crystalline (definite shape, sharp melting point) and amorphous (irregular, no sharp MP).
- →Seven crystal systems and 14 Bravais lattices.
- →SC: CN=6, packing=52.4%. BCC: CN=8, packing=68%. FCC: CN=12, packing=74%.
- →HCP: packing efficiency 74% — most efficient.
- →Schottky defect: missing ions (density decreases). Frenkel defect: ion shifts to interstitial position (density unchanged).
- →n-type semiconductor: extra electrons (doped with group 15). p-type: electron holes (doped with group 13).
Formulas & Equations
For SC: a = 2r
For BCC: 4r = a√3
For FCC: 4r = a√2
Density: ρ = ZM/(a³Nₐ)
Exam Tips
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Know packing efficiencies and coordination numbers for SC, BCC, FCC.
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Density formula: Z = number of atoms per unit cell — 1 for SC, 2 for BCC, 4 for FCC.
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Distinguish between Schottky and Frenkel defects.