Difference Between Linear and Nonlinear Molecules

The key difference between linear and nonlinear molecules is that linear molecules have a chemical structure which is in a straight line whereas nonlinear molecules have a zig-zag or cross-linked chemical structure.

All the molecules we know can be divided into two types as linear molecules and nonlinear molecules depending on the shape of the molecule. If the chemical structure of a molecule has linear geometry, which appears to be a straight line, then it is a linear molecule. All other molecules are categorized as nonlinear molecules.

CONTENTS

1. Overview and Key Difference
2. What are Linear Molecules
3. What are Nonlinear Molecules
4. Side by Side Comparison – Linear vs Nonlinear Molecules in Tabular Form
5. Summary

What are Linear Molecules?

Linear molecules are compounds having the linear geometry. That means; these linear molecules have their atomic connectivity in a straight line. All the atoms in the molecule are arranged in a perfect line.

Figure 01: Linear Geometry

In linear geometry, there are usually three atoms in the molecule – a central atom is bonded to two other atoms via covalent bonds. The two atoms in the opposite sides of this molecule are called ligands bound to the centre. The bond angle of the linear molecule is 180°.

When considering organic compounds having the linear geometry, there is a carbon atom at the centre of the molecule, and the ligands bind with the carbon atom via double or triple bonds. Here, the central atom has sp hybridization of atomic orbitals—E.g. acetylene. In addition to these, there are linear inorganic compounds as well; for example, carbon dioxide, hydrogen cyanide, etc.

What are Nonlinear Molecules?

Nonlinear molecules are compounds that have a geometry other than linear geometry. That means; these molecules are not linear, and their atoms are not arranged in a straight line. The shape of these molecules depends on the hybridization of the atomic orbitals of the atoms in the molecule. Some of the possible shapes are V-shaped molecules, angular, trigonal planar, tetragonal molecules, pyramidal molecules, etc. The bond angles of these molecules differ from each other according to the shape.

Figure 02: Nonlinear Molecules

When considering complex molecules such as polymers, they also can be linear or nonlinear. Most of the nonlinear polymers are branched or cross-linked polymers. Branched polymers have side groups or pendant groups attached to a straight line of atoms. Cross-linked polymers have cross-links between straight lines of polymer chains, forming network structures.

What is the Difference Between Linear and Nonlinear Molecules?

All the molecules we know can be divided into two types as linear molecules and nonlinear molecules depending on the shape of the molecule. The key difference between linear and nonlinear molecules is that linear molecules have a chemical structure which is in a straight line whereas nonlinear molecules have a zig-zag or cross-linked chemical structure.

Acetylene, carbon dioxide, hydrogen cyanide, etc. are some examples of linear molecules whereas branched and cross-linked polymers such as vulcanized rubber are examples of nonlinear molecules.

The following table summarizes the difference between linear and nonlinear molecules.

Summary – Linear vs Nonlinear Molecules

All the molecules we know can be divided into two types as linear molecules and nonlinear molecules depending on the shape of the molecule. The key difference between linear and nonlinear molecules is that linear molecules have a chemical structure which is in a straight line whereas nonlinear molecules have a zig-zag or cross-linked chemical structure.

Reference:

1.“Linear Molecular Geometry.” Wikipedia, Wikimedia Foundation, 4 Apr. 2020, Available here.
2. “Cross-Linked Polymer.” Cross-Linked Polymer – an Overview | ScienceDirect Topics, Available here.

Image Courtesy:

1. “Linear-3D-balls” (Public Domain) via Commons Wikimedia
2. “Cross-linked DNA by nitrogen mustard” By Simon Caulton – Own work (CC BY-SA 3.0) via Commons Wikimedia

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