Definition : When a molecule containing a H atom is linked to a highly electronegative atom (like N, O, F), this atom attracts the shared pair of electrons more and so this end of the molecule becomes slightly negative while the other end (i.e., H-end) becomes slightly positive. The negative pole of one molecule attracts the positive pole of the other molecule and so on and as a result, a weaker bond is formed between them. This bond is called hydrogen bond. It is represented by dot¬ted lines as shown in figure.
As a result of Hydrogen bonding, a H-atom links the two electronegative atoms simultaneously, one by a covalent bond and the other by a hydrogen bond. Hence it is said to form a hydrogen bridge. Hydrogen bond is a weak bond, but it is stronger than van-der Waals forces.