Saturday, February 28, 2015
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.
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