The crystal lattice is the symmetrical three-dimensional structural arrangements of atoms, ions or molecules (constituent particle) inside a crystalline solid as points. It can be defined as the geometrical arrangement of the atoms, ions or molecules of the crystalline solid as points in space.
Characteristics of Crystal Lattice:
- In a crystal lattice, each atom, molecule or ions (constituent particle) is represented by a single point.
- These points are called lattice site or lattice point.
- Lattice sites or points are together joined by a straight line in a crystal lattice.
- When we connect these straight lines we can get a three-dimensional view of the structure. This 3D arrangement is called Crystal Lattice also known as Bravais Lattices.
Unit Cell is the smallest part (portion) of a crystal lattice. It is the simplest repeating unit in a crystal. The entire lattice is generated by the repetition of the unit cell in different directions.
Parameters of a Unit Cell
There are six parameters of a unit cell. These are the 3 edges which are a, b, c and the angles between the edges which are α, β, γ. The edges of a unit cell may be or may not be perpendicular to each other.
Types of Unit Cell
Primitive Unit Cells: When the constituent particles occupy only the corner positions, it is known as Primitive Unit Cells.
Centered Unit Cells: When the constituent particles occupy other positions in addition to those at corners, it is known as Centred Unit Cell. There are 3 types of Centered Unit Cells:
- Body Centred: When the constituent particle at the centre of the body, it is known as Body Centred Unit cell.
- Face Centred: When the constituent particle present at the center of each face, it is known as Face Centered Unit cell.
- End Centred: When the constituent particle present at the center of two opposite faces, it is known as an End Centered Unit cell.