Unit cell

Definition

A unit cell is the smallest repeating unit of a crystalline solid that shows the entire structure's symmetry and properties. It defines the crystal's lattice structure and is characterized by its geometry and atomic arrangement.

5 Must Know Facts For Your Next Test

1. A unit cell's dimensions are defined by three edge lengths (a, b, c) and three angles (α, β, γ).
2. There are seven crystal systems based on unit cell geometry: cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic.
3. The coordination number of a unit cell refers to how many nearest neighbor atoms surround a given atom within the cell.
4. The volume of a unit cell can be calculated using its edge lengths and angles.
5. Unit cells can be classified into primitive (P), body-centered (I), face-centered (F), and base-centered (C) types.

Review Questions

• What are the seven crystal systems based on unit cell geometry?
• How do you calculate the volume of a unit cell?
• What is meant by the coordination number in a unit cell?

Related terms

Crystal Lattice: A three-dimensional arrangement of atoms or molecules in a crystalline solid.

Bravais Lattice: Fourteen distinct lattice structures which describe all possible symmetric arrangements of points in three-dimensional space.

Coordination Number:

The number of nearest neighbor atoms or ions surrounding an atom or ion in a crystal lattice.