Dispersion Force - The intermolecular force

[srmeier]

(I would like to put an idea of mine to rest) About one year ago I took a college chemistry course in which I learned about intermolecular forces. The weakest of these intermolecular forces, I learned, was the dispersion force (also called London force). This force was discovered by Fritz W. London. Here I would like to quote my text:

"Dispersion forces are the result of fluctuations in the electron distribution within molecules or atoms. Since all atoms and molecules have electrons, they all exhibit dispersion forces... An instantaneous dipole on anyone atom induces instantaneous dipoles on neighboring atoms, which then attract one another..."

-by CHEMISTRY: A Molecular Approach, Nivaldo J. Tro (pg.466)

This (at the very least) seems a lot like gravity. So, why can't we explain gravity as just another aspect of the electromagnetic force which manifests itself through millions of intermolecular electron fluctuations?

Thanks,

 

[mikeph]

This is not gravity, it is due to the dipole, and is an electric force.

 

[srmeier]

This is not gravity, it is due to the dipole, and is an electric force.

I understand that they are classified as different things. I just feel as though if dispersion forces can account for atoms attracting one another then why do we need gravity?

 

[pzona]

Dispersion forces are instantaneous, and they form dipole moments, not permanent dipoles. A simple way of putting this is that, depending on the location of the electron, the dipole is either turned on or off like a switch.

Gravity, on the other hand, is universal and permanent. It is a constant force between any two masses regardless of electrical charge (or lack thereof). We need gravity in addition to the electrical intermolecular forces simply because they are two different forces.

You might be interested in looking into the "Theory of Everything" for more information on the unification of forces. This is one of the biggest and most important problems in physics today.

 

[srmeier]

Dispersion forces are instantaneous, and they form dipole moments, not permanent dipoles. A simple way of putting this is that, depending on the location of the electron, the dipole is either turned on or off like a switch.

Gravity, on the other hand, is universal and permanent. It is a constant force between any two masses regardless of electrical charge (or lack thereof). We need gravity in addition to the electrical intermolecular forces simply because they are two different forces.

You might be interested in looking into the "Theory of Everything" for more information on the unification of forces. This is one of the biggest and most important problems in physics today.

I read that book and liked it a lot (although i didn't understand most of it), Thanks!

 

[pzona]

Keep reading! It'll start to make more sense the more you study it, I promise.