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London Forces or van der Waals Forces    Dipole-Dipole Attraction    Hydrogen Bonding

 

van der Waals Forces and London Dispersion Forces

 

 

 

 

Simplified Explanation

van der Waals Forces are very weak forces of attraction between molecules resulting from: 

  • London Forces (Fritz London 1930),  are weak IMF that arise from momentary dipoles occurring due to uneven electron distributions in neighboring molecules as they approach one another

  • the weak residual attraction of the nuclei in one molecule for the electrons in a neighboring molecule. 

 
A momentary dipole is all it takes to cause weak attraction in nonpolar molecules.Cl2, Br2 and I2 are all nonpolar so any attractions that occur (liquid and solid phases) are caused by van der Waals forces.

****This weak intermolecular attraction is why nonpolar gases in our atmosphere can form liquids under extreme pressure and low temperatures.

The more electrons that are present in the molecule, the stronger the dispersion forces will be. 

Dispersion forces are the only type of intermolecular force operating between non-polar molecules, for example, dispersion forces operate between 

  • hydrogen (H2) molecules

  • chlorine (Cl2) molecules

  • carbon dioxide (CO2) molecules

  • dinitrogen tetroxide (N2O4) molecules

  • methane (CH4) molecules

 

Another contribution to chemistry.

van der Waals equation

Johannes Van der Waals was interested in the kinetic theory of gases and fluids, and his primary work was to develop an equation which applied to real gases, unlike that of Robert Boyle which assumes that there are no attractive forces between molecule and that molecules have zero volume.
In reality, molecules have a small volume and attractive forces exist between them. Van der Waals introduced these properties into the theory by means of two constants, which were specific to each gas:

(P + a/v2)(v-b) = RT  , where a and b are constant for a particular gas.

Van der Waals was awarded a Nobel prize in 1910 for his work on the equation of state of gases and liquids.

The weak, electrostatic attractions between atoms were named Van der Waals forces in his honor.

from-http://www.chemsoc.org/timeline/pages/1920.html

London Forces or van der Waals Forces    Dipole-Dipole Attraction    Hydrogen Bonding

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