Intermolecular forces are electromagnetic forces which act between molecules. Listed in order of decreasing strength, these forces are:
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2 Hydrogen Bonding 3 Dipole-Dipole Interactions 4 London Dispersion Forces |
This is an interactions that occurs between charged species, like charges will have a repulsive force while opposite charges will have an attractive force.
H20---H-O-H
Hydrogen bonds are found throughout nature. Hydrogen bonds give water its unique properties, which allowed life to develop on earth; hydrogen bonds are also the intermolecular force that binds together the two strands in a molecule of DNA
Dipole-Dipole interactions are the forces that occur between two molecules with permanent dipoles. These work in a similar manner to ionic interactions but are weaker because only partial charges are involved. An example of this can be seen in hydrochloric acid:
(+)(-) (+) (-)
Also called London forces or Van der Waals forces, these involve the attraction between temporaily induced dipoles in nonpolar molecules. This polarization can be induced either by a polar molecule or by the repulsion of negatively charged electron clouds in nonpolar molecules. An example of the former is chlorine dissolving in water:
Ionic Interactions
Hydrogen Bonding
hydrogen bonding can be formed when a hydrogen atom is bound to a highly electronegative atom such as nitrogen, oxygen, or fluorine. The hydrogen atom has a partial positive charge and can interacts with another electronegative atoms found in a different molecule (again N, O, or F). This results in a stabilizing interaction that loosely binds the two molecules together. A common example is water:Dipole-Dipole Interactions
H-Cl-----H-ClLondon Dispersion Forces
(+)(-)(+) (-) (+)
[Permanent Dipole] H-O-H-----Cl-Cl [Induced Dipole]
An example of the second scenario is found in molecular chlorine: (+) (-) (+) (-)
[Induced Dipole]Cl-Cl------Cl-Cl [Induced Dipole]
HI