Chapter 11 – Solid State (JEE Chemistry)
1. What is Solid State?
Solid state deals with the study of solids, particularly crystalline solids, where particles are arranged in an ordered and repeating pattern.
2. Classification of Solids
| Type | Characteristics |
|---|---|
| Crystalline | Long-range order, sharp melting point |
| Amorphous | No long-range order, gradual softening |
3. Crystal Lattice
A crystal lattice is a regular three-dimensional arrangement of points in space representing particle positions.
4. Unit Cell
Unit cell is the smallest repeating unit of a crystal lattice which generates the entire crystal.
Types of Unit Cells
- Primitive Unit Cell
- Body-Centered Cubic (BCC)
- Face-Centered Cubic (FCC)
5. Number of Atoms per Unit Cell
| Unit Cell | Atoms per Cell |
|---|---|
| Simple Cubic | 1 |
| BCC | 2 |
| FCC | 4 |
6. Packing Efficiency
Simple Cubic
Packing efficiency = $52.4\%$
Body-Centered Cubic
Packing efficiency = $68\%$
Face-Centered Cubic
Packing efficiency = $74\%$
7. Density of Unit Cell
$$\text{Density} = \frac{Z \times M}{N_A \times a^3}$$
Where:
$Z$ = number of atoms per unit cell
$M$ = molar mass
$a$ = edge length
$N_A$ = Avogadro number
8. Voids in Crystals
- Tetrahedral void
- Octahedral void
Number of Voids
Tetrahedral voids = $2N$
Octahedral voids = $N$
Octahedral voids = $N$
9. Radius Ratio Rules
| Coordination Number | Radius Ratio |
|---|---|
| 4 | $0.225 - 0.414$ |
| 6 | $0.414 - 0.732$ |
| 8 | $0.732 - 1.0$ |
10. Imperfections in Solids
Point Defects
- Schottky defect
- Frenkel defect
Electrical Defects
Creation of electron holes due to missing electrons.
Impurity Defects
Addition of foreign atoms to improve conductivity.
11. Electrical Properties of Solids
| Type | Conductivity |
|---|---|
| Conductors | High |
| Semiconductors | Moderate |
| Insulators | Low |
12. Band Theory
Electrical behavior depends on energy gap between valence band and conduction band.
13. Semiconductors
n-Type
Doping with group 15 elements (P, As).
p-Type
Doping with group 13 elements (B, Al).
14. Magnetic Properties
- Diamagnetic
- Paramagnetic
- Ferromagnetic
15. Dielectric Properties
Insulating solids that develop polarization in an electric field.
16. JEE Exam Tips
- Remember packing efficiencies
- Practice density numericals
- Learn defect differences clearly
- Band theory questions are frequent