Difference Between Lattice and Unit Cell

Key Difference – Lattice vs Unit Cell
 

A lattice is a regular structure made of many small units known as unit cells. A unit cell is the smallest representative unit of a lattice comprising of all the components that can be found repeating all over the lattice structure. The key difference between lattice and unit cell is that a lattice is a regular repeated three-dimensional arrangement of atoms, ions, or molecules in a metal or other crystalline solid whereas a unit cell is a simple arrangement of spheres (atoms, molecules or ions) that resemble the repeating pattern of a lattice.

CONTENTS

1. Overview and Key Difference
2. What is a Lattice
3. What is a Unit Cell
4. Relationship Between Lattice and Unit Cell
5. Side by Side Comparison – Lattice vs Unit Cell in Tabular Form
6. Summary

What is a Lattice?

A lattice is a regular repeated three-dimensional arrangement of atoms, ions, or molecules in a metal or other crystalline solid. A unit cell of lattice represents the repeating arrangement of the lattice; the unit cell is the smallest unit in a lattice that has all the chemical components in the lattice.

A lattice can be formed due to covalent bonds between atoms, ionic bonds between ions or intermolecular forces between molecules. An example of covalent network lattices is diamond. There, carbon atoms are bonded to each other via covalent bonds, making a complex network structure. Sodium chloride lattice is a typical example of an ionic lattice. There, sodium cations and chloride anions are arranged in a complex network forming an ionic lattice. Water molecules can also form a lattice; ice. There, hydrogen bonds between water molecules can cause the formation of a lattice that resembles the structure of diamond. Most of the metals are also arranged in lattice structures.

There are lattice defects in almost all the lattices. A defect is an irregularity in the lattice system. There are two main types of lattice defects; Frenkel defect and Schottky defect. In Frenkel defects, an atom or ion in the lattice leaves its original location and occupies a different site in the same lattice. A Schottky defect occurs when oppositely charged ions leave their original location.

When considering the thermodynamics of a lattice, the lattice energy is a measure of the energy contained in the crystal lattice of a compound, equal to the energy that would be released if the component ions were brought together from infinity.

There are 14 types of lattices. These forms are categorized based on the arrangement of atoms, molecules or ions in the unit cell. The lattice types are given in the following table along with the category.

What is a Unit Cell?

A unit cell is a simple arrangement of spheres (atoms, molecules or ions) that resemble the repeating pattern of a lattice. A unit cell is considered as a box structure. This box contains all the chemical components that are present all over the lattice. A unit cell is a 3D structure, and it is described using lattice parameters. Lattice parameters are the lengths between edges and the angles of the unit cell.

1. lengths between edges of the unit cell are denoted by symbols a, b and c
2. angles of the unit cell are denoted by symbols alpha(α), beta(β) and gamma(γ)

A unit cell can be in various shapes depending on the angles and the lengths between cell edges. It is the building block of a lattice. There are 7 types of cubic unit cells. The names of these unit cell shapes and their dimensions are given in the below table.

What is the Relationship Between Lattice and Unit Cell?

• A unit cell is the smallest representative unit of a lattice. It gives all the components and their arrangement that is being repeated throughout the lattice structure.

What is the Difference Between Lattice and Unit Cell?

Summary – Lattice vs Unit Cell

A lattice is a complex network structure having small units attached to each other. These small units are known as unit cells. The difference between lattice and unit cell is that a lattice is a regular repeated three-dimensional arrangement of atoms, ions, or molecules in a metal or other crystalline solid whereas a unit cell is a simple arrangement of spheres (atoms, molecules or ions) which resemble the repeating pattern of a lattice.

Reference:

1.“Unit Cell.” Chemistry LibreTexts, Libretexts, 31 Jan. 2017. Available here 
2.“Symmetry, Crystal Systems and Bravais Lattices.” Symmetry, Crystal Systems and Bravais Lattices | Physics in a Nutshell. Available here 
3.“12.1 Crystal Lattices and Unit Cells.” Chemistry LibreTexts, Libretexts, 30 Jan. 2018. Available here  
4.“Lattice.” Merriam-Webster, Merriam-Webster.Available here  

Image Courtesy:

1.’2790370′ by DavidZydd (Public Domain) via pixabay
2.’UnitCell’By Mcpazzo – Own work, (Public Domain) via Commons Wikimedia