Van der Waals forces

[Aerlinn]

Can anyone tell me what they are? 🙂

[victor]

it’s an intermolecular force created by some electronegative and electropositive atoms..

[Aerlinn]

Ok… can you explain that more?

[victor]

what can I explain more than that?? Van Der waals is an intermolecular force..that’s all…or maybe anyone wanna help??

[Aerlinn]

So… are the electronegative and electropositive atoms attracted to each other in this? And what do you mean by ‘some’?

[victor]

Um, aome atoms have excesses electrons and some of them also loss some electrons…after that, they began to get attracted each other.
in common language, some are nucleophylics and some are electrophylics..

[baikuza]

van der waals forces is caused by the fluctuation on the shell of atoms in molecules.
you know, for example between H and Cl. Cl is more elektronegative so that electron can be found more in the Cl atom’s side.

then this makes H has fewer electron in it’s shell. quiet clear?

[Aerlinn]

Do you mean Cl, being electronegative wants an electron and H gives it one? I’m confused. It sounds like ionic bonding…

[victor]

Arrgh..what Baikuza said was tye tendency of drawed electron in intramolecular covalent bonding..it’s truly different from VDW force..
let me explain it with ZBS then:
Imagine there are two molecule of acetic acid(CH3COOH)….if we write the simple structural formula it would be R-COOH. Um, you can see that O atom which is bound with only one binding chain have the remaining of valence electron.
Because of those excesses valence electron, some H atom from another acetic acid molecule can be drawed closer one another and forms O—H (remember, this is only a weak binding).

PS: you have to differ between intramolecular and intermolecular forces. Try to understand both of them.

Clear now?? I hope so..:wink:

[baikuza]

then because of the electron moves not at a perfect circle…. i mean the moves look like the wave that is move at quite constant interval… you can imagine it as angle at the end of evangelion manga volume 9…(+.+)
even this forces happen on the non-polar molecules… they have a little forces to other molecules/atom(s)…..this can attach other molecules/atom(s). the forces multiply by 10to minus17 of the distance between the related molecules…
okay.. i gave a wrong example.. the right is CCl4, Cl2,… etc.
… sorry.. i do not include this at my post above…

[victor]

Naah, the definition and example that you gave were for INTRAMOLECULAR FORCE but what Aerlinn ask was the definition of Van Der Waals Forces or in other words..INTERMOLECULAR FORCES…

[Aerlinn]

I think I get you… So it’s similar to the hydrogen bonds between molecules, the Van der Waals forces? It’s a weak bond, as in, the molecules are attracted to each other?

And… what’s the difference between intramolecular and intermolecular forces? 😕

[victor]

Yup, hydrogen bond is one of them….
Intramolecular force is a force energy that’s contained inside one molecule…Example, covalent bond and ionic bond.
i.e. CH4

Intermolecular force is a force energy that’s formed by at least 2 molecule.
i.e. CH3COOH—OHOCCH3

[zami’87.]

Van der Waals forces are much weaker than forces that enable hydrogen bonds.VDW f can act between nonpolar molecules and temporarily form dipoles(consequence of moving of electrons). eg in H2,Cl2,F2…

[Aerlinn]

quote :

Van der Waals forces are much weaker than forces that enable hydrogen bonds.

You contradicted what Victor said. Are Hydrogen bonds Van der Waals forces? :S

quote :

Intramolecular force is a force energy that’s contained inside one molecule…Example, covalent bond and ionic bond.
i.e. CH4

Intermolecular force is a force energy that’s formed by at least 2 molecule.
i.e. CH3COOH—OHOCCH3

Thanks for explaining that to me 🙂

[victor]

Hydrogen bond are one of the intermolecular force (means it’s one group with VDW force) but the energy stored inside the hydrogen bond is more than any other intermolecular force. This is because H atom get binded with O atom which is very electronegative.

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