A crystal lattice is a regular, three-dimensional arrangement of constituent particles (atoms, ions, or molecules) represented by points (lattice points).
A unit cell is the smallest repeating unit of a crystal lattice that, when stacked in all three directions, generates the entire crystal.
Key numbers to memorise:
- Total crystal systems = 7
- Total Bravais lattices = 14
- For NEET: focus on 3 cubic unit cells (SC, BCC, FCC) + HCP
Unit cell parameters:
- Edge lengths: a, b, c
- Interaxial angles: α, β, γ
- For cubic systems: a = b = c, α = β = γ = 90°
Atom sharing at different positions:
| Position | Number of cells sharing | Contribution per cell |
|---|---|---|
| Corner | 8 | 1/8 |
| Face centre | 2 | 1/2 |
| Body centre | 1 | 1 |
| Edge centre | 4 | 1/4 |