Difference between Van der Waal's and Dipole-dipole

[dmission]

Hi -- I'm wondering if someone can please clarify to me the difference between Van Der Waals bonds (intermolecular) and Dipole-dipole bonds (also intermolecular), I believe. Would greatly appreciate it, as I can't seem to figure them out. Thanks!

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[thestrokes14]

Van der waals forces are just special cases of dipole-dipole interactions. Van der waals refers to transient charges (instantaneous dipoles due to moving electrons). For those small instances, the molecules actually contain dipoles and thus interact with other molecules with instantaneous dipoles. You can understand why Van der waals forces are weak...they are pretty much instantaneous and don't last very long.

 

[tmh]

Van der waals forces are just special cases of dipole-dipole interactions. Van der waals refers to transient charges (instantaneous dipoles due to moving electrons). For those small instances, the molecules actually contain dipoles and thus interact with other molecules with instantaneous dipoles. You can understand why Van der waals forces are weak...they are pretty much instantaneous and don't last very long.

I think you're referring to dispersion forces (http://en.wikipedia.org/wiki/London_dispersion_force)

and that van der waals force is a broad category for intermolecular forces, which includes dipole-dipole and dispersion forces.

 

[thestrokes14]

I think you're referring to dispersion forces (http://en.wikipedia.org/wiki/London_dispersion_force)

and that van der waals force is a broad category for intermolecular forces, which includes dipole-dipole and dispersion forces.

Yes, thanks! I got that mixed up. Van der waals forces are basically synonymous with dipole-dipole interactions. Dispersion forces is what I originally described, which is indeed a special case of dipole-dipole.