Topics - Hydrogen Bonding
Hydrogen bonding is a term given to extremely strong polar molecular interactions. The energy associated with very strong polar interactions approaches that of a chemical bond and, for that reason has been termed a ‘hydrogen bonding’, but, in fact, the interaction is reversible and no actual chemical bond is formed. There are, broadly, three ways in which molecules can interact with each other without actually reacting. Molecules can interact dispersively by London’s dispersion forces, they can interact electrically between dipoles and induced dipoles and they can interact ionically as between oppositely charged ions. The term hydrogen is included in the term used for this very strong interaction process because the hydrogen atom is usually associated with very strong polar groups that exhibit very strong molecular interaction (e.g., the hydroxyl groups in alcohols, phenols and, in particular water itself). Water would not be a liquid at normal temperatures and pressures if it were not due to the strong hydrogen bonding that takes place between the water molecules themselves. The strong hydrogen bonding that causes the very strong association of water molecules is reflected in the high latent heat of fusion and excessively large latent heat of vaporization of water. Hydrogen bonding also accounts for the relatively high boiling point and density of methanol.