What is the Difference Between Induced Dipole and Permanent Dipole

A dipole is a molecule or object that has two opposite poles: a positive pole and a negative pole. This separation of charge creates a small region with an electric field. There are two main types of dipoles as: permanent dipoles and induced dipoles.

What is the difference between induced dipole and permanent dipole? A permanent dipole is a molecule’s built-in imbalance of charge, while an induced dipole is a temporary imbalance created by external factors.

Key Areas Covered

1. What is Induced Dipole 
      – Definition, Features
2. What is Permanent Dipole
      – Definition, Features 
3. Similarities Between Induced Dipole and Permanent Dipole
      – Outline of Common Features
4. Difference Between Induced Dipole and Permanent Dipole
      – Comparison of Key Differences
5. FAQ: Induced Dipole and Permanent Dipole
      – Answers to Frequently Asked Questions

Key Terms

Induced Dipole, Permanent Dipole, Polarity

What is Permanent Dipole

Electronegativity is the measure of an atom’s ability to attract electrons towards itself in a chemical bond. A permanent dipole occurs due to the differences in electronegativity among the atoms that form the molecule. In other words, it occurs due to the uneven distribution of electron density.

When atoms with different electronegativities bond, the electrons are more attracted to the atom with higher electronegativity; hence, a partial negative charge is created on the more electronegative atom and a partial positive charge is created on the less electronegative atom of the molecule. Due to the charge separation on the molecule, a permanent dipole is created.

Figure 1: Two Molecular Dipoles

The magnitude of the permanent dipole is measured in Debye (D). It is a vector quantity. The difference in electronegativity between bonded atoms and the distance between them decides the magnitude of the dipole moment. A larger dipole moment means a stronger dipole-dipole interaction. Molecules such as ammonia, water, and hydrogen chloride are some examples of molecules having permanent dipoles.

What is Induced Dipole

An induced dipole is a temporary separation of charge within an atom or molecule caused by an external electric field. When a polar molecule (one with a permanent dipole) approaches a nonpolar molecule (one without a permanent dipole), the positive end of the polar molecule attracts the electrons in the nonpolar molecule. This causes a slight shift in the electron cloud of the nonpolar molecule, creating a temporary, uneven distribution of charge. This induced dipole is weaker than a permanent dipole but still contributes to intermolecular forces.

Figure 2: Induced Dipole

The polarity of the inducing molecule and the polarizability of the induced molecule are the factors that determine the strength of the induced dipole. Polarizability refers to the ease of distortion of an electron cloud in a molecule. Larger molecules with more electrons are generally more polarizable.

Similarities Between Induced Dipole and Permanent Dipole

1. Both contribute to intermolecular forces.
2. Both phenomena are based on the movement or distribution of electrons within a molecule.

Difference Between Induced Dipole and Permanent Dipole

Definition

A permanent dipole arises from inherent electronegativity differences between atoms in a molecule, while an induced dipole is created by an external electric field or the proximity of a polar molecule.

Change

A permanent dipole is constant and not changing, but in an induced dipole, the dipole is temporary and changes.

Strength

A permanent dipole is stronger than an induced dipole.

Occurs In

Permanent dipole occurs in polar molecules, whereas induced dipole occurs in any type of molecule.

Leads to

Permanent dipole leads to dipole-dipole interactions, whereas induced dipole leads to London dispersion forces.

External Factors

Permanent dipole is independent of the external factors whereas induced dipole depends on the external electric field or the presence of polar molecules.

Conclusion

Permanent dipoles are intrinsic and stable features of polar molecules or molecules with polar bonds, while induced dipoles are temporary and arise in response to external electric fields or nearby polar molecules. This is the basic difference between induced dipole and permanent dipole.

FAQ: Induced Dipole and Permanent Dipole

1. What is the difference between dipole-dipole and ion-induced dipole?

Dipole-dipole interactions occur between two polar molecules with permanent dipoles. Ion-induced dipole interactions involve a permanent ion and a nonpolar molecule, where the ion induces a temporary dipole in the nonpolar molecule.

2. Why is it called an induced dipole?

An induced dipole is called so because it’s a temporary dipole created in a normally nonpolar molecule. This occurs when a nearby ion or polar molecule distorts the electron cloud of the nonpolar molecule, causing a temporary separation of charge.

3. What is the difference between LDF and induced dipole?

LDF (London dispersion forces) and induced dipoles are basically the same thing. Both refer to weak intermolecular forces that arise due to temporary fluctuations in electron distribution, creating temporary dipoles in molecules.

4. What is an example of a dipole-induced dipole force?

A dipole-induced dipole force occurs between a polar molecule (like water) and a nonpolar molecule (like methane). The polar molecule’s electric field temporarily distorts the electron cloud of the nonpolar molecule, creating a temporary dipole and a weak attraction between them.

5. Is hydrogen bonding stronger than induced dipole-induced dipole?

Yes, hydrogen bonding is stronger than induced dipole-induced dipole interactions. Hydrogen bonds involve a specific interaction between hydrogen and highly electronegative atoms (N, O, F), creating a strong dipole. Induced dipole forces are generally much weaker as they rely on temporary fluctuations in electron distribution.

Reference:

1. “Induced Dipole – An Overview.” Science Direct.
2. “Permanent Dipole – An Overview.” Science Direct.

Image Courtesy:

1. “Schematic of the electrostatic interaction between two dipolar molecules” By Cnrowley – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Induced Dipole Caused by Sedementation1” By Fruitninja446 – Own work (CC BY-SA 3.0) via Commons Wikimedia