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Non Life Sciences => Chemistry => Topic started by: bashir2008 on 10/04/2009 14:27:38

Title: What are van der Waals attractions?
Post by: bashir2008 on 10/04/2009 14:27:38

Dear all

1- I want to understand more about Van der Waals force . how does it happen and what is the importance of it... could you please support your answer with some drawings as well?
2- What is the drag force ?

Hope there are some people who can assist me

Thanks

Title: Re: What are van der Waals attractions?
Post by: Chemistry4me on 11/04/2009 03:55:58

Drag force is forces that oppose the relative motion of an object through a fluid (a liquid or gas).

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

Title: Re: What are van der Waals attractions?
Post by: Chemistry4me on 11/04/2009 04:02:45

For van der Waals:

http://www.chemguide.co.uk/atoms/bonding/vdw.html

Separate page for hydrogen bonding:

http://www.chemguide.co.uk/atoms/bonding/hbond.html#top

Title: Re: What are van der Waals attractions?
Post by: Raghavendra on 12/04/2009 09:08:32

Vander  bonding easy to learn

Title: Re: What are van der Waals attractions?
Post by: Chemistry4me on 12/04/2009 11:57:20

Obviously it is easier to learn it than to spell it? [:)]

Title: What are van der Waals attractions?
Post by: Raghavendra on 13/04/2009 07:22:49

LOL  [;D] [;D] Ya you are right

Title: What are van der Waals attractions?
Post by: bashir2008 on 13/04/2009 11:03:45

Thanks for answering the question

Title: What are van der Waals attractions?
Post by: lightarrow on 13/04/2009 14:14:54

Quote from: Chemistry4me on 11/04/2009 04:02:45

For van der Waals:

http://www.chemguide.co.uk/atoms/bonding/vdw.html

Separate page for hydrogen bonding:

http://www.chemguide.co.uk/atoms/bonding/hbond.html#top

Just for curiosity, why did you link the page of hydrogen bonding?

Title: What are van der Waals attractions?
Post by: Chemistry4me on 13/04/2009 14:16:42

In a textbook it (hydrogen-bonding) went under the same heading (as instantaneous dipole-dipole, permanent dipole-dipole etc...) of: van der Waals forces.

Title: What are van der Waals attractions?
Post by: lightarrow on 13/04/2009 14:27:11

Quote from: Chemistry4me on 13/04/2009 14:16:42

In a textbook it (hydrogen-bonding) went under the same heading (as instantaneous dipole-dipole, permanent dipole-dipole etc...) of: van der Waals forces.

Ok, you can throw away that text [:)].  They are completely different things.

Title: What are van der Waals attractions?
Post by: Chemistry4me on 13/04/2009 14:30:50

Oh really? [???] That'll mean...have I been learning the wrong stuff? [:)]
So they are a completely different form of intermolecular attraction?

Title: What are van der Waals attractions?
Post by: lightarrow on 13/04/2009 14:36:15

Quote from: Chemistry4me on 13/04/2009 14:30:50

Oh really? [???] That'll mean...have I been learning the wrong stuff? [:)]
So they are a completely different form of intermolecular attraction?

Yes:
Van der Waals interactions are much weaker (per unit surface of molecules) than hydrogen bonding and, furthermore, they are dipole interactions due to instantaneous dipole induction, whyle hydrogen bonding are due to permanent dipoles; furthermore hydrogen bonding is directional (just think about ice' structure), Van der Waals is not.

Title: What are van der Waals attractions?
Post by: Chemistry4me on 13/04/2009 14:46:31

Okay, I see what you mean. Cheers lightarrow.