Difference Between Induced Dipole and Permanent Dipole

The key difference between induced dipole and permanent dipole is that induced dipole moment can change when the factors affecting the dipole moment are changed, whereas changing external factors do not affect the permanent dipole moment.

Intermolecular forces are the interactions between molecules. These interactions may include both attractions and repulsions. The attractive intermolecular forces cause the formation of compounds such as crystals. The most common attractive intermolecular forces include hydrogen bonding, ionic bonding, ion-induced dipole interactions, ion-permanent dipole interactions, and Van der Waal forces.

CONTENTS

1. Overview and Key Difference
2. What is Induced Dipole 
3. What is Permanent Dipole
4. Side by Side Comparison – Induced Dipole vs Permanent Dipole in Tabular Form
5. Summary

What is Induced Dipole?

Induced dipole refers to the dipole moment created in a nonpolar compound due to the effect of an ion nearby. Here, the ion and nonpolar compound form an interaction called the ion-induced dipole interaction. The charge of the ion induces the creation of a dipole (a chemical species with polarization). In addition, the ion can repel the electron cloud of the nonpolar compound by getting closer to the nonpolar compound.

Both negative and positive charged ions can cause this type of dipole moments. For example, let’s take a negatively charged ion inducing a dipole moment in a nonpolar compound. The side of the nonpolar compound that is closer to the ion gets a partial positive charge because the electron cloud is repelled by the negative electrons of the ion. This, in turn, gives the other side of the nonpolar compound a partial negative charge. Therefore, an induced dipole is created in the nonpolar compound.

Likewise, a positive charge ion attracts the electron cloud, giving a partial negative charge to the side of the nonpolar compound that is closer to the positive ion.

What is Permanent Dipole?

Permanent dipole refers to the dipole moment that originally occurs in a compound due to uneven electron distribution. Therefore, a polar compound contains a permanent dipole moment.

Here, a polar compound contains two different atoms with different electronegativity values. Due to this reason, the more electronegative atom(s) in the polar compound attracts bond electrons than less electronegative atom(s). This creates a state in which a more electronegative atom gets a partial negative charge while the less electronegative atom gets a partial positive charge. This establishes a permanent dipole in the molecule.

What is the Difference Between Induced Dipole and Permanent Dipole?

Induced dipole refers to the dipole moment that creates in a nonpolar compound due to the effect of an ion nearby. In contrast, permanent dipole refers to the dipole moment that originally occurs in a compound due to uneven electron distribution. Moreover, induced diploe occurs in nonpolar compounds, while permanent dipole occurs in polar compounds. Therefore, the key difference between induced dipole and permanent dipole is that induced dipole moment can change when the factors affecting the dipole moment are changed whereas changing external factors do not affect the permanent dipole moment.

The below infographic tabulates the difference between induced dipole and permanent dipole.

Summary – Induced Dipole vs Permanent Dipole

Induced dipole refers to the dipole moment that creates in a nonpolar compound due to the effect of an ion nearby. In contrast, permanent dipole refers to the dipole moment that originally occurs in a compound due to uneven electron distribution. So, the key difference between induced dipole and permanent dipole is that induced dipole moment can change when the factors affecting the dipole moment are changed, whereas changing external factors do not affect the permanent dipole moment.

Reference:

1.“Ion – Induced Dipole Interactions.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available here.
2. “Intermolecular Force.” Wikipedia, Wikimedia Foundation, 29 Jan. 2020, Available here.

Image Courtesy:

1. “Schematic of an instantaneous-dipole — induced-dipole interaction” By Christopher Rowley – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Schematic of the electrostatic interaction between two dipolar molecules” By Cnrowley – Own work (CC BY-SA 4.0) via Commons Wikimedia