vdw forces and london dispersion forces

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heartshaker
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I know how vdw forces work, but I'm confused between london dispersion forces and vdw forces. Are the london dispersion forces a type of vdw forces? If so, what is the difference?

Any help is appreciated xx
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HateOCR
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London force and VDW forces are the same thing they just have different names. They happen when the electron cloud is not even dispersed between two bonded atoms at an instant. i.e an electron cloud could be closer to one atom than another at any instant giving it a temporary delta - charge. This means the other atoms bonded to it will bd delta +. The VDW force is the attraction between D+ and D- but between different molecules.
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heartshaker
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(Original post by HateOCR)
London force and VDW forces are the same thing they just have different names. They happen when the electron cloud is not even dispersed between two bonded atoms at an instant. i.e an electron cloud could be closer to one atom than another at any instant giving it a temporary delta - charge. This means the other atoms bonded to it will bd delta +. The VDW force is the attraction between D+ and D- but between different molecules.
Ok so the 2 are the same? Are they both induced dipole-dipole forces?
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HateOCR
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(Original post by heartshaker)
Ok so the 2 are the same? Are they both induced dipole-dipole forces?
Yes. Permanent dipole-dipoles happen between atoms that are bonded with a large difference in electronegativity. E.g H-F will have a permanent dipole as F has a stronger “electron pulling power” than H.
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heartshaker
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(Original post by HateOCR)
Yes. Permanent dipole-dipoles happen between atoms that are bonded with a large difference in electronegativity. E.g H-F will have a permanent dipole as F has a stronger “electron pulling power” than H.
Right this all makes sense now! Thank you so much!
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HateOCR
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(Original post by heartshaker)
Right this all makes sense now! Thank you so much!
No problem.
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Pigster
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(Original post by heartshaker)
I'm confused between london dispersion forces and vdw forces.
So were several exam boards.

OCR A and AQA used to think that VdW were idid (London forces).

They now (correctly) realise that idid and pdpd are both types of VdW.

OCR A (the one I know best) will avoid using the term VdW in exams and will probably be asking questions in such as way as to make VdW NOT an allowable answer, i.e. idd or pdd would be expected but not either.
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