Intermolecular Interactions Types

The attractive and repulsive forces that emerge between the molecules of a substance are known as intermolecular forces or IMF. These forces mediate interactions between individual molecules of a material.

Forces that exist between molecules are referred to as intermolecular forces. Intermolecular forces dictate the majority of the material’s physical qualities. Intermolecular forces are responsible for the formation of condensed states of matter. The particles that make up solids and liquids are held together by intermolecular forces, which influence several physical properties of matter in these two states.

Hydrogen bonding

The attraction between a hydrogen atom bonded to an element with strong electronegativity, usually nitrogen, oxygen, or fluorine, and another of these elements is known as a hydrogen bond. A strong electrostatic dipole-dipole interaction is typically used to describe the hydrogen bond. However, it shares some characteristics with covalent bonding, such as being directional (stronger than a Van der Waals force interaction), producing interatomic distances (shorter than the sum of their Van der Waals radii), and usually involving a small number of interaction partners (valence).

Intermolecular interactions types

An intermolecular force exists when one molecule’s positive (or protons) components attract the negative (or electrons) components of another molecule. This force determines the physical and chemical properties of a substance. The strength of its intermolecular forces determines the boiling point of a substance; the stronger the intermolecular forces, the higher the boiling point. By comparing the boiling temperatures of different substances, we can compare the intensity of intermolecular forces. This is because the heat acquired at the boiling point of the substance is used to break these intermolecular connections and transform the liquid to vapour.

The following interactions influence intermolecular forces:

1. Dipole-Dipole Interactions

When two polar molecules are close to one another, dipole-dipole interaction occurs. Forces between dipoles occur between molecules with permanent dipole-dipole forces. One molecule’s positively charged portion attracts the negatively charged portion of another molecule. This is a common intermolecular force since many molecules are polar.

Examples of dipole-dipole forces:

A dipole-dipole interaction occurs when one molecule’s atoms are attracted to the oxygen atoms of another molecule—for instance, the interaction between two sulphur dioxide (SO2) molecules. 

Hydrogen bonding, for example, is a type of dipole-dipole interaction that always involves hydrogen. A hydrogen atom of one molecule is attracted to an electronegative atom of another molecule, such as an oxygen atom in water.

2. Ion-Dipole Interactions

When an ion collides with a polar molecule, it forms an ion-dipole interaction. The charge of the ion determines which component of the molecule attracts and repels in this situation. The negative part of a molecule attracts a cation or positive ion, whereas the positive part repels it. The positive part attracts an anion or negative ion, whereas the negative part repels it.

Example of Ion-dipole interaction:

The ion-dipole interaction is exemplified by a Na+ ion and water (H2O) interaction. The sodium ion and oxygen atoms are attracted while sodium and hydrogen are repelled.

3. Ion-Induced Dipole Interactions

A nonpolar molecule is polarised by an ion placed near it in this form of interaction. When nonpolar molecules gain a charge, they behave like induced dipoles. The ion-induced dipole interaction occurs between an ion and an induced dipole.

4. Dipole Induced Dipole Interaction

A dipole-induced dipole attraction occurs when a polar molecule generates a dipole in an atom or a nonpolar molecule by disrupting the configuration of electrons in the nonpolar species.

5. Dispersion Forces or London Forces

LDF, London forces, dispersion forces, instantaneous dipole forces, induced dipole forces, or the induced dipole-induced dipole force are all names for the London dispersion force.

The intermolecular force between two nonpolar molecules, known as the London dispersion force, is the weakest of the intermolecular forces. The electrons of one molecule are drawn to the nucleus of the other, but the electrons of the other molecule repel them. A dipole is formed when the electron clouds of molecules are deformed by attracting and repulsive electrostatic interactions.

The interaction between two methyl groups (-CH3) is an example of London dispersion force.

Example of Dispersion Forces or London Forces:

The interaction between nitrogen gas (N2) and oxygen gas (O2) molecules is a second example of London dispersion force. The atoms’ electrons aren’t the same as the electrons of other atoms.

Conclusion

As previously stated, intermolecular forces observed between atoms and molecules can be phenomenologically defined as occurring between permanent and instantaneous dipoles. Alternatively, one could look for a fundamental, unifying theory that can explain a wide range of interactions, including hydrogen bonding, Van der Waals forces, and dipole-dipole interactions.