Intermolecular 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.

• 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.

Requires:

• 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.