Different Types of Intermolecular Forces

Types of intermolecular forces

The attractive force that exists between the positive components (protons) and the negative components (electrons) of atoms and molecules of a substance (solid, liquid, gaseous) is termed as intermolecular force. Various physical and chemical properties of a substance depend on this force. The boiling point of a substance is higher when it has strong intermolecular forces. By comparing the boiling point of different substances we can compare the intermolecular forces of substances because the heat absorbed in boiling point is used to break these intermolecular forces of substance and to convert the liquid into vapour.

The intermolecular forces depend on the following interactions:

  1. Dipole-dipole interactions: Dipole -dipole interactions are the attractive forces among the polar molecules. Polar molecules have permanent dipoles which are formed due to electronegativity difference between the molecules associated in a covalent bond. The partially positive portion of one molecule is thus attracted to partially negative portion of the other molecule. For example: Dipole -dipole interaction occurs in HCl molecule. Chlorine is comparatively more electronegative than hydrogen and thus it acquires a partial negative charge, whereas hydrogen acquires a positive charge. The dipole-dipole interaction then takes place between the HCl molecules.
  2. Ion dipole interactions: It is similar to that of dipole-dipole interaction except the fact that interaction takes place among an ion and a polar molecule. For example: When NaCl is mixed with water in a beaker, then there are polar water molecules and sodium and chlorine ions in the beaker. The polar water molecules get attracted towards Cl ion and Na+

The strength of this interaction depends on:

  • the magnitude of the dipole moment and size of a polar molecule
  • the size and charge of an ion

3.  Ion induced dipole interactions: In this a non polar molecule is polarized by an ion placed near it. The non-polar molecules get charged and behave as an induced dipole. This interaction between an ion and an induced dipole is known as ion induced dipole interaction.

4. Dipole induced dipole interaction:It is similar to that of ion induced dipole interaction. But in this a non-polar molecule are induced 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.