Why are non-polar molecules attracted to each other?

  • #1

Main Question or Discussion Point

Okay guys I have a question that does not make sense to me.
My teachers, and even the chem and bio textbooks, have often said that polar molecules bond with each other, and non-polar molecules bond with each other.

I do get why polar molecules can form bonds, which is due to the e- arrangement, allowing for uneven spread of e-.

However, why do non-polar molecules bond with each other? Ofcourse the explanation is temporary dipoles, but all molecules exhibit that.
So why would, lets say, CH4 (l) mix with itself better than water? (Not considering molecular size)
Yea it's not polar so it mainly forms LDF w/ H2O, but it only forms LDF with itself too. And if anything, it should form stronger bonds with H2O because H2O at least exhibits polarity, and the C-H bond is not super un-polar, so a CH4-H2O bond would be more dipole-dipole than a CH4-CH4. Unless I am wrong in something I have stated (in which case please correct me).

So guys what's the explanation for this?
 

Answers and Replies

  • #2
Borek
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Simple answer: they don't bond.

Longer answer: in the mixture of polar and non-polar molecules the lowest energy system will have non-polar molecules combined, as it allows polar molecules to make more bonds between them (less "molecule surface" is lost to contact with non-polar molecules). It doesn't mean non-polar molecules bond, but it looks as if they did.
 
  • #3
DrClaude
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My teachers, and even the chem and bio textbooks, have often said that polar molecules bond with each other, and non-polar molecules bond with each other.
This is, unfortunately, a common but misleading way to put things. If you consider the interaction of water molecules and oil molecules, you will find that the attraction between a water and an oil molecule is greater than the attrition between two oil molecules. The reason that water and oil separate is that the attraction of two water molecules is so much greater that separation is a lower energy situation.

Looks like @Borek beat me to it...
 
  • #4
Makes sense thanks guys.
 

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