Difference Between Intermolecular and Intramolecular Forces

Main Difference – Intermolecular vs Intramolecular Forces

Intermolecular and intramolecular forces are the two types of forces that hold individual molecules and atoms together. These forces control the movement of molecules and atoms. Both types of forces determine the chemical and physical characteristics of substances. The main difference between intermolecular and intramolecular forces is that intermolecular forces exist between the molecules themselves, whereas intramolecular forces exist between atoms within a molecule. In addition, there are many more differences between these forces.

This article examines, 

1. What are Intermolecular Forces?
       – Definition, Features, Characteristics

2. What are Intramolecular Forces?
       – Definition, Features, Characteristics

3. What is the difference between Intermolecular and Intramolecular Forces?

What are Intermolecular Forces

Intermolecular forces are forces that bind individual molecules in a substance due to their positive and negative charges. Intermolecular forces are attractive forces, but not chemical bonds. Thus, intermolecular forces are much weaker than intramolecular forces. These forces determine the physical characteristics of a substance. One of their most important physical characteristics is the ability to determine the state of a substance – whether it is solid, liquid or gas. These forces are responsible for the random motion of gasses and the existence of liquids and solids as they hold liquid and solid molecules together. Hence, intermolecular forces determine the melting and boiling point of the matter. Melting or boiling point is proportional to the strength of intermolecular forces. i.e., the higher the melting or boiling point, the stronger the intermolecular forces. At a given temperature, the strengths of intermolecular forces of gas, liquid and solid are as follows.

                        Gas < Liquid < Solid

There are three types of intermolecular forces known as dipole-dipole forces, London dispersion forces and hydrogen bonding forces. All these bonds occur due to electric charges resulting from the arrangement of electrons and nuclei in the molecules. Among the three types, hydrogen bonds are the strongest form of intermolecular bonds. Water molecules are held by hydrogen bonds due to the presence of partial charges at specific locations on the molecules.

What are Intramolecular Forces

Forces that hold atoms in a molecule are called intramolecular forces. These forces are responsible for the formation of chemical bonds. Thus, intramolecular forces are much stronger than intermolecular forces. Intramolecular interactions occur when two atoms share electrons or donate/gain electrons to/from another atom. When electrons are shared between two atoms, the bond is called a covalent bond. When one atom gives/ gain electron, the bond is called an ionic bond. Intramolecular forces determine chemical parameters of a substance. Metal bonds are also classified as a type of intramolecular force.

Difference Between Intermolecular and Intramolecular Forces

Definition

Intermolecular forces are the forces that hold molecules in a substance.

Intramolecular forces are the forces that hold atoms in a molecule.

Strength

Intermolecular forces are weaker than intramolecular forces.

Intramolecular forces are stronger than intermolecular forces.

Determination of Properties      

Intermolecular forces determine the state of matter (solid/liquid/gas) and their physical properties such as melting/ boiling point etc.

Intramolecular forces determine chemical behavior of a substance.

Nature of Forces

Intermolecular forces are attractive forces.

Intramolecular forces are chemical bonds.

Examples

Intermolecular forces are categorized into dipole-dipole forces, London dispersion forces and hydrogen bonding forces.

Intramolecular forces are categorized into covalent, ionic and metal bonds.

Image Courtesy:

“Ionic Bonds” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia 

Reference:

Myers, R. The Basics of Chemistry. N.p.: Greenwood Publishing Group, 2003. Print. CliffsNotes AP chemistry: with CD-ROM. Hoboken, NJ: Wiley, 2009. Print. Kelter, P. B., M. D. Mosher, and A. Scott. Chemistry: The Practical Science. Vol. 10. N.p.: Cengage Learning, 2008. Print. Rogers, D. L., S. R. Goode, and D. W. Balle. Chemistry: Principles and Practice. N.p.: Cengage Learning, 2009. Print.

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