What Are Intermolecular Forces?

Intermolecular forces are the attractive forces between molecules that hold them together. There are four types of intermolecular forces: hydrogen bonds and ionic, dipole and induced dipole forces.

There are two types of molecular forces, intramolecular and intermolecular forces. Intramolecular bonds hold the individual atoms of a molecule together while intermolecular forces are found between the molecules themselves.

Ionic forces are electrostatic forces that exist between charged molecules. A positively charged molecule and a negatively charged molecule are held together by these forces.

Dipole forces are found in covalent molecules that are polar. Polar molecules have atoms of different electronegativities that are arranged asymmetrically around a central atom. For example, in ammonia, nitrogen has a high electronegativity and pulls the shared electrons in the bonds towards itself and develops a partial negative charge, while hydrogen, which has a lower electronegativity, develops a partial positive charge. When several molecules of ammonia, or any polar covalent molecule, are present in close proximity to each other, they are held together by dipole forces between the partial positive charge of one molecule and a partial negative charge of another molecule.

Hydrogen bonding is a special type of dipole force that exists in molecules in which hydrogen is bound to a highly electronegative atom, such as nitrogen, fluorine or oxygen. Hydrogen atoms gain a partial positive charge and are attracted to the electronegative atoms with a partial negative charge in a different molecule.

Induced dipole forces are found in non-polar covalent molecules. The electron clouds shift to form temporary dipoles within the molecule. The temporary partial positive charges momentarily are attracted to the temporary partial negative charge of a different molecule, after which the electron clouds shift again to create a different dipole. These temporary forces are the weakest of all intermolecular forces