Fractional distillation

[Mukilab]

What does one mean when one says that longer chains of hydrocarbons have stronger attraction hence higher boiling point?

 

Is there some different force holding molecules together? I thought the strong and weak nuclear forces wre only for the nucleus...

[Mr Skeptic]

Yes, there are a whole set of intermolecular forces. One that you always have is due to electron density fluctuating, so as to cause small temporary attractions. Another is polar molecules, where electron density is permanently skewed, so that bits of the molecule act as slightly positive while other bits act as slightly negative. In the most extreme case of this, with hydrogen and either oxygen, nitrogen, or fluorine, this is called hydrogen bonding.

 

Larger molecules also move slower at a given energy, and have more atoms each that can have intermolecular interactions.

[Horza2002]

The force Mr Skeptic is describing due to electron density fluctuations is called Van der Waals forces if you want to go read about them.

 

http://en.wikipedia.org/wiki/Van_der_Waals_force