Chemical bonding -HYDROGEN BONDING

 

HYDROGEN BONDING

·     ·       In 1920, Latimer and Rodebush introduced the idea of "hydrogen bond" to explain the nature of association in liquid state of substances like water, hydrogen fluoride, ammonia, formic acid, etc.

     ·       Hydrogen bond can be defined as the attractive force which binds hydrogen atom of one molecule with the electronegative atom (F, O or N) 

     ·       It exerts in polar molecule or molecule having polar group.

     ·       This bond is represented by dotted line (---------) while solid represents the covalent bond.

     ·       The magnitude of the hydrogen bonding depends on the physical state of the compound.

     ·        order of  increasing strength of hydrogen bond in various physical state as

        gas < Liquid< solid  

        Type of hydrogen bonding-

         a)       Intermolecular hydrogen bonding: This type of bonding results between the positive and negative ends of different molecules of the same or different substances. Example-

   a) H^δ+ — F^δ--------H^δ+ — F^δ+--------H^δ+ — F^δ-

   b) H^δ+ — F^δ--------H^δ+ — O —H^δ+-------H^δ+ — F^δ       

        b).    Intramolecular hydrogen bonding: This type of bonding results between hydrogen and an electronegative element both present in the same molecule.

Importance of Hydrogen bond-

   ·      It helpful to explain that H2O exits in liquid state while H2S exists in gaseous state since in H2O, oxygen is more electronegative element than Sulphur in H2S therefore oxygen has ability to form H-bond with other water molecules. so it exists.

   ·      Ortho-nitrophenol has low boiling point than para-nitrophenol since P-nitrophenol form intermolecular hydrogen bond which is stronger than intra molecular hydrogen bond which is formed by ortho-nitrophenol.

     ·      Solubility of compound in water can be explained on the basis of h-bonding. Example alcohol is soluble in water but oil not. Because alcohol forms H-bond with water but oil does not form.