CHEMICAL BOND- HYDROGEN BOND

CHEMICAL BOND- HYDROGEN BOND

THE POLAR COVALENT BOND BETWEEN HYDROGEN ATOMS AND OTHER ATOMS.

forms when a hydrogen atom with a partial positive charge attracts the partial negative charge of neighbouring electronegative atoms.

                 most often larger oxygen or nitrogen atoms.

Thus HYDROGEN bonds result from attraction of oppositely charged parts of molecules.

Are weak compared to Ionic or Covalent bond

They cannot bind atoms into molecules 


Even though single Hydrogen bonds are weak, very large molecules may contain thousands of these bonds.

Acting collectively,  
           these bonds provide considerable strength and 
             help determine the three dimensional shape of large molecules.

eg.

In H2O- water

Hydrogen bonds occur because hydrogen atoms in 1 molecule are attracted to the partial negative charge of the oxygen atom in another water molecule.

                     H  - O -     H
                             /        /
                            H      O - H
                                     /        
                                   H  -  O
                                           /
                                        H

SURFACE TENSION

A measure of the difficulty of stretching or breaking the surface of a liquid.

COHESION

The tendency of like particles to stay together.

The hydrogen bond that link neighbouring water molecules give water considerable COHESION

The cohesion  of water molecules creates a very high SURFACE TENSION

The boundary between water and air, waters surface tension is very high 
   because the water molecules are attracted to one another than they are attracted to the molecules in the air.

eg.

In breathing
  A thin film of watery fluid coats the air sacs of the lungs.

 So each  inhalation must have enough force to overcome the opposing effect of surface tension
    - as the air sacs stretch and enlarges when taking in air.