Intermolecular Forces

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  • Created by: ava.scott
  • Created on: 13-04-14 15:14

Van der Waal forces

  • Weak, instantaneous forces between molecules caused by electron drift.
  • These instaneous dipoles cause weak attractions between atoms/molecules.
  • If electron density is not equally distributed, a dipole will occur.  
  • In turn, the negative pole will repel the electrons in a nearby atom or molecule, creating another dipole- the cycle repeats itself.
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Dipole-dipole interactions

  • Dipoles are caused by a difference in electronegativity between the two bonded atoms. e.g. H-Cl. The Cl will be negatively charged as the Chlorine is more electronegative.
  • If two polar molecules are near eachother, their oppositely charged poles will attract.
  • These are stronger than VDW forces.


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Hydrogen Bonds


  • A hydrogen bonded to nitrogen, oxygen or flourine.
  • and a lone pair.

The electronegativity difference is great, so the hydrogen is very positively charged. This means its very attracted the electron-dense-lone pair on the N, O or F.

They are the strongest of intermolecular forces, and explain why water is liquid at room temperatures.

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