Lattice Points: Overview, Questions, Preparation

Lattice points are essential since they provide a systematic way to describe the three-dimensional arrangement of particles in a crystal. This arrangement is critical in understanding the physical and chemical properties of solids. Lattice is a regular repeated 3D arrangement of atoms, ions, or molecules in a crystalline solid. Each point in a lattice is called a lattice point. Lattice point represents the constituent particle of a solid which may be an atom or a molecule.

There are primarily three types of lattice points:

Primitive Lattice Points: These points represent the positions of the smallest repeating unit, called the unit cell, in a crystal lattice.
Face-Centered Lattice Points: These points are found at the center of each face of the unit cell and are often associated with cubic unit cells.
Body-Centered Lattice Points: These points are located at the center of the unit cell and are commonly found in body-centered cubic (BCC) unit cells.

Let us learn about different types of crystal lattices, including:

• Simple Cubic (SC) Lattice 
• Body-Centered Cubic (BCC) Lattice 
• Face-Centered Cubic (FCC) Lattice

Simple Cubic (SC) Lattice

In the simple cubic structure there is only one lattice point at each corner of the cube-shaped unit cell.

Body-Centered Cubic (BCC) Lattice

A BCC unit cell has atoms at each corner of the cube and an atom at the centre of the structure. Body-centered cubic (BCC) is defined as a crystal structure that consists of a cube-shaped unit cell with atoms located at the corners and in the center of the cube. In this structure, each atom is surrounded by eight nearest neighbours located at the corners of the cube.

Face-Centered Cubic (FCC) Lattice

An FCC unit cell has atoms at all the corners of the crystal lattice and at the centre of all the faces of the cube. The atom present at the face-center is shared between 2 adjacent unit cells and only 1/2 of each atom belongs to an individual cell.

In the context of lattice points, the coordination number represents the number of nearest neighboring particles to a given lattice point. Different types of lattices have different coordination numbers.

Crystal Systems

Lattice points and unit cells are used to classify crystals into seven crystal systems, which are further categorized based on the angles and lengths of their unit cell edges. These systems include cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and rhombohedral (trigonal) systems.