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help on bonding - HSN forum

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help on bonding


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#1 sarmad

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Posted 22 December 2005 - 09:29 PM

hi guys im am struggling on bonding. i dont really understand Dipole-dipole attractions, if anyone understands it can u please explain it to me thanks

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#2 dfx

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Posted 22 December 2005 - 09:44 PM

Do you mean instantaneously induced dipole-dipole interactions (Van der Waals forces)?

If so, consider say Chlorine where 2 Cl atoms are covalently bonded by sharing a pair of electrons. The chlorine molecules then are held together by van der waals forces. This occurs because you have to remember that electrons are constantly moving, and at any given time, there is the possibility that all the electrons gather at one end of the Cl2 molecule. Thus you have a dipole - a negative dipole in the region where the electrons have gathered and a positive dipole in the other relatively "empty" end. So the negative and positive dipoles of all of the molecules attract each other.

There is major confusion because ALL INTERmolecular forces (within molecules) are known as Van der Waals forces. These also include dipole-dipole interactions.

Ok hope that was right lol. Bonding and periodicity is one of the - if not THE - toughest bit of the Higher.

#3 UncleJohnny

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Posted 02 February 2006 - 10:38 PM

QUOTE(dfx @ Dec 22 2005, 09:44 PM)
Do you mean instantaneously induced dipole-dipole interactions (Van der Waals forces)?

If so, consider say Chlorine where 2 Cl atoms are covalently bonded by sharing a pair of electrons. The chlorine molecules then are held together by van der waals forces. This occurs because you have to remember that electrons are constantly moving, and at any given time, there is the possibility that all the electrons gather at one end of the Cl2 molecule. Thus you have a dipole - a negative dipole in the region where the electrons have gathered and a positive dipole in the other relatively "empty" end. So the negative and positive dipoles of all of the molecules attract each other.

There is major confusion because ALL INTERmolecular forces (within molecules) are known as Van der Waals forces. These also include dipole-dipole interactions.

Ok hope that was right lol. Bonding and periodicity is one of the - if not THE - toughest bit of the Higher.

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it could also be permament polar polar covalent bonds....


#4 YIC

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Posted 07 February 2006 - 05:22 PM

Bonding can be quite tough to get your head around.

INTRAmolecular bonding:

1) Metallic bonds
2) Ionic Bonds (when e-neg values are really different)
3) Polar Covalent Bonding (when e-neg values are different, but not too different)
4) Non-Polar Covalent Bonding (when e-neg values are the same)

INTERmolecular bonding

1) van der Waals: weak forces arising from electrostatic attractions between TEMPORARY and INDUCED dipoles

temporary dipoles: a non polar molecule, which may become temporarily polar due to the outer electrons being unevenly spread around the molecule (i.e. more electrons in one end than the other, making one end more negative than the other)

Induced dipoles: a molecule that has been attracted by the temporary dipole

(this causes van der waals)

2) Permanent dipole - Permanent dipole attractions: additional e'static attractions between molecules with polar covalent bonds. (i.e. happens between polar molecules)

3) Hydrogen Bonding: additional e-static attractions between highly polar molecules which consist of Hydrogen bonded to an atom of very high electronegativity - F, N or O
(an example of hydrogen bonding is a water molecule bonding to another water molecule)

(hydrogen bonding is the strongest intermolecular bond, while van der waals is the weakest)

This is basically what Higher bonding is all about. So it is nothing too complicated, you just need to break it down and realise what the hell is going on.

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#5 YIC

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Posted 10 February 2006 - 12:44 PM

QUOTE(dfx @ Dec 22 2005, 09:44 PM)
There is major confusion because ALL INTERmolecular forces (within molecules) are known as Van der Waals forces. These also include dipole-dipole interactions.

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Are you sure that is right? You get different Intermolecular forces. (AFAIK, Hydrogen bonding is not a type of van der waals tongue.gif ) Maybe you mean that van der vaals exists between ALL molecules?

#6 dfx

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Posted 10 February 2006 - 09:08 PM

Well, Hydrogen Bonding is an exception. tongue.gif

I don't know, I'm pretty sure I recall reading somewhere that VdW forces are generalized.... hmm...

#7 YIC

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Posted 11 February 2006 - 12:25 PM

QUOTE(dfx @ Feb 10 2006, 09:08 PM)
Well, Hydrogen Bonding is an exception. tongue.gif

I don't know, I'm pretty sure I recall reading somewhere that VdW forces are generalized.... hmm...

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hmm....not sure man....perhaps you heard that they exist in all molecules? I think someone like Ally should clear this up.

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