Intermolecular Forces: Definition and Its Types

Intermolecular forces include electromagnetic forces of attraction or repulsion that act between atoms and other types of neighbouring particles, such as atoms or ions, to mediate interaction between molecules.  The majority of matter’s chemical and physical properties are due to intermolecular forces. The higher the intermolecular forces, for example, the higher the boiling point. We can safely deduce that an element’s boiling point is proportional to the strength of its intermolecular forces.

Definition of Intermolecular forces

“Intermolecular forces are electrostatic in nature, meaning they are created by the interaction of positively and negatively charged species. Intermolecular interactions, like covalent and ionic bonds, are made up of both attractive and repulsive components.”

As electrostatic interactions decrease fast as the distance between molecules increases, solids and liquids have the most intermolecular interactions increases. Only at very high pressures do these interactions become important for gases, where they are responsible for observed deviations from the ideal gas law.

Types of Intermolecular Forces

1. Dispersion Forces

2. Dipole – Dipole Forces

3. Dipole–Induced Dipole Forces

Dispersion Forces

The electrons that orbit molecules can move and their charge distributions can change over time. The molecule’s positive end might be positive, whereas the negative end can be negative. When two opposite charges are close to each other, they form a transient dipole. It is possible for one molecule to be attracted to another when they come into contact. Dispersion forces are at work when the electrons from the first molecule sense a pull toward the positive charge of the second molecule. However, the attraction isn’t really strong. Dispersion forces are stronger than dipole-dipole forces.

Example: Dispersion forces can be seen in compounds like bromine (Br2) or chlorine (Cl2). Methane is another common example (CH4). Because there are no permanent dipoles in methane, the only forces are dispersion forces. Because they attract particles, dispersion forces aid the transformation of nonpolar molecules into liquids or solids.

The atoms on both sides of the covalent link are identical, the electrons in the covalent bond are equally shared, and the bond is nonpolar. As a result, other than dispersion forces, diatomic bromine has no intermolecular forces.

Dipole – Dipole Forces

The electrostatic forces between two permanent polar molecules are known as dipole-dipole forces or dipole-dipole interactions. The positive end of one molecule is generally attracted to the negative end of another. As a result, the two molecules become closer, increasing the substance’s stability. Because there is no transfer or sharing of electrons, this interaction differs from a regular ionic or covalent bond.

When two positive or negative dipoles approach each other, they form an attractive intermolecular connection, whereas two positive or negative dipoles form a repellent intermolecular interaction. The Van der Waals forces are a combination of dipole-dipole interactions and London dispersion forces. Electrostatic interactions include dipole-dipole interactions, ion-ion interactions, and ion-dipole interactions.

As the number of molecules involved grows, dipole interactions become increasingly intricate. Molecules in a liquid move freely, which means they interact with one other in both attractive and repulsive ways.

Example: Two hydrogen (H) atoms are bonded to an oxygen (O) atom in water (H2O).

Two hydrogen (H) atoms are joined to one oxygen (O) atom in H2O. The O-H bond gains a permanent dipole as a result. The hydrogen atom has a partial positive charge, while the oxygen atom has a partial negative charge. As a result, the H from one molecule attracts the O from another, creating a dipole-dipole interaction.

 Dipole–Induced Dipole Forces

When a polar molecule induces a dipole in an atom or a nonpolar molecule by disrupting the arrangement of electrons in the nonpolar species, a dipole-induced dipole attraction occurs.

A dipole-induced dipole attraction develops when a polar molecule creates a weak attraction, a dipole in an atom or a nonpolar molecule by disrupting the non-polar species’ electron configuration.

The existence of a polar molecule is required for the dipole–induced-dipole interaction to occur. The presence of the polar molecule’s partial charges causes the electron distribution of the other molecule to be polarised, or distorted.

 Noble gases, for example, become polarised in the presence of polar molecules, as seen in the diagram above.

 Conclusion

In this article we learned Dipole-dipole, dipole-induced dipole, dispersion forces, and hydrogen bonding are all examples of intermolecular forces. In gases, intermolecular forces of attraction are the weakest, while thermal energy is the strongest. Solids have the largest intermolecular forces of attraction, whereas thermal energy is the lowest. Liquids have two sorts of energies that are halfway between gases and solids.