Intermolecular Force Ionic Interactions Hydrogen Bonding

These are fundamentally electrostatic interactions (ionic interactions, hydrogen bond, dipole-dipole interactions) or electrodynamic interactions (van der Waals/London forces). Electrostatic interactions are classically described by Coulomb's law, the basic difference between them are the strength of their charge. Ionic interactions are the strongest with integer level charges, hydrogen bonds have partial charges that are about an order of magnitude weaker, and dipole-dipole interactions also come from partial charges another order of magnitude weaker. A very approximate strength order would be:

1 Ionic Interactions

These are interactions that occur between charged species ( ions). Like charges repel, while opposite charges attract.

2 Hydrogen Bonding

Hydrogen bonds are found throughout nature. They give water its unique properties so important to life on earth. Hydrogen bonds between hydrogen atoms and nitrogen atoms of adjacent base pairs provide the intermolecular force that bind together the two strands in a molecule of DNADeoxyribonucleic acid DNA is a nucleic acid which carries genetic instructions for the biological development of all cellular forms of life and many viruses. DNA is sometimes referred to as the molecule of heredity as it is inherited and used to propagate.

3 Dipole-Dipole Interactions

Dipole-dipole interactions, also called Keesom interactions after Willem Hendrik KeesomWillem Hendrik Keesom ( 1876- 1956) was a Dutch scientist who, in 1926, invented a method to solidify helium. He was previously a student of Heike Kamerlingh Onnes, who had been the first to liquify helium (a feat for which Kamerlingh Onnes received a Nob who produced the first mathematical description in 1921, 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 acidProperties General Name Hydrogen chloride Chemical formula H Cl Appearance Colourless liquid Physical Formula weight 36. 5 amu Melting point 203. 15 K (-70 °C) Boiling point 382 K (109 °C) Density 1. 2 ×103 kg/ m3 (liquid) Solubility 70 g in 100g water Th:

4 London Dispersion Forces

Also called London forces or Van der Waals forceIn chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer only to London forces: those forces which arise from induced rather than permanent dipoles. The forces are nams, these involve the attraction between temporarily 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:

(+)(-)(+) (-) (+) [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]

5 See also

polymerA polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. The monomers can be identical, or in complex polymers such as proteins the monomers have one or more substituted chemical groups, this gives them Chemistry

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