Intermolecular Forces?

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PrabUppal
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#1
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#1
How do you know when to mention van der waals in an exam question?
Also,I'm confused as to where van der waals forces are,like are they only in covalent molecules etc,I just find apply my knowledge on this topic to exam questions hard,any help is appreciated.
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Kallisto
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(Original post by PrabUppal)
How do you know when to mention van der waals in an exam question?
Also,I'm confused as to where van der waals forces are,like are they only in covalent molecules etc,I just find apply my knowledge on this topic to exam questions hard,any help is appreciated.
Remember that Van der waals forces as intermolecular forces are a result of ineracting electrons. Just imagine a shell with electrons in it. The side of a shell with a surplus of electons has a negative charge, while the side with a lack of electrons has a positive charge. And so the different charges come into being. Those different charges attracts each other, and so the atoms. This leads to a bond of those atoms. Here is a good picture to van der waals forces between two atoms.

So these intermolecular forces are always in existence when different charges are forming bonds. The crystalline bonds of salts are a good example for that. The bonds in salts consists of a positive charge (Na+) and a negative one (Cl-).
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voltz
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#3
Whenever the question mentions melting or boiling point, it wants you to talk about intermolecular forces
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Kallisto
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(Original post by voltz)
Whenever the question mentions melting or boiling point, it wants you to talk about intermolecular forces
It could also be asked for the bonds of certain molecules, the bonds of water molecules for instance. Can remember me to be asked for those forces in such a context.
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PrabUppal
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so do induced dipoles occur in non polar molecules and permanent dipoles occur in non polar molecules?What would I say in an exam?
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PrabUppal
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(Original post by Kallisto)
It could also be asked for the bonds of certain molecules, the bonds of water molecules for instance. Can remember me to be asked for those forces in such a context.
How would i know if a molecule has an induced or permanent dipole,I'm not sure how id be able to tell what the intermolecular forces are
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alow
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#7
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(Original post by PrabUppal)
so do induced dipoles occur in non polar molecules and permanent dipoles occur in non polar molecules?What would I say in an exam?
Polar molecules have a permanent dipole which can induce dipoles in nearby molecules .

Non-polar molecules can have instantaneous dipoles which can induce dipoles in nearby molecules (Dispersion).

Both of these are "van der Waals" forces.
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