HYDROGEN BONDING

The electrostatic force of attraction between partially positively charged hydrogen in a polar molecule and an electronegative atom is called hydrogen bond.
It is represented by dotted line as shown below.

H--------X

where X is an electronegative atom.
Characteristics of Hydrogen bond 
1) The nature of H-bonding is purely electrostatic.
2) The hydrogen atom must be covalently bonded to a highly electronegative atom in order to acquire sufficient positive charge to participate in hydrogen bonding.
3) The electronegative atom should possess high charge density so as to attract positively charged hydrogen atom effectively. Thus H-bonding is observed with smaller and highly electronegative atoms such as F, O and N.
4) The hydrogen bond is stronger than van der Waal's forces of attraction. However it is weaker than the covalent bond and ionic bond.
5) The strength of H- bond is directly proportional to the electronegativity of electronegative atom. Thus the strengths of hydrogen bonds with different electronegative atoms varies as follows:
H------F > H------O > H-------N

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