Types of Intermolecular Forces
An intermolecular force is an attractive force that arises between the positive components (or protons) of one molecule and the negative components (or electrons) of another molecule. Various physical and chemical properties of a substance are dependent on this force. The boiling point of a substance is proportional to the strength of its intermolecular forces – the stronger the intermolecular forces, the higher the boiling point.
By comparing the boiling points of different substances, we can compare the strengths of their intermolecular forces. This is because the heat absorbed by the substance at its boiling point is used to break these intermolecular forces and to convert the liquid into vapour.
The intermolecular forces depend on the following interactions:
- Dipole-dipole interactions: Dipole -dipole interactions are attractive forces among polar molecules. Polar molecules have permanent dipoles which are formed due to differences in the electronegativities of the atoms that are associated in a covalent bond. The partially positive portion of one molecule is attracted to the partially negative portion of another molecule.
Example: Dipole -dipole interactions occur in HCl molecules. Chlorine is comparatively more electronegative than hydrogen and it, therefore, acquires a partial negative charge (whereas hydrogen acquires a partial positive charge). The dipole-dipole interaction then takes place between the HCl molecules.
- Ion-dipole interactions: These interactions are similar to dipole-dipole interactions except for the fact that they arise between ions and polar molecules. Example: When NaCl is mixed with water in a beaker, the polar H2O molecules are attracted to the sodium and chloride ions in the beaker. The strength of this interaction depends on:
- The magnitude of the dipole moment
- Size of the polar molecule
- The size and charge of an ion
3. Ion induced dipole interactions: In this type of interaction, a non-polar molecule is polarized by an ion placed near it. The non-polar molecules, upon obtaining a charge, behave as induced dipoles. This interaction between an ion and an induced dipole is known as ion-induced dipole interaction.
4. Dipole induced dipole interaction: These interactions are similar to ion-induced dipole interactions. However, the differentiating factor is that non-polar molecules are transformed into induced dipoles due to the presence of a polar molecule nearby.
5. Dispersion forces or London forces: It operates for a short distance and it is the weakest force. This kind of force arises due to movement of electrons thus creating temporary positive and negative charged regions.
This was just a brief introduction to the different type of intermolecular interaction. To learn more about it, download BYJU’S – The Learning App.