Chemistry unit 2

Could somebody explain intermolecular forces to me and why they are so weak.

you have three types of intermolecular forces: hydrogen bonding, dipole-dipole and Van der Waals
they are all weaker than covalent, metallic and ionic bonding.
in covalent bond the separate atoms share electrons to make a molecule.
intermolecular forces are forces between molecules, they are not properly bonded, as in sharing electrons.
in VDWs (the weakest force), the electron density (think of electrons around an atom as a cloud of negative charge called the electron density) they are constantly moving around and making small changes in the charge at different places around the molecule, so at any one time 1 part of an atom might be negative so it is attracted to another part of a molecule which is positive. this is how they stay together. (i hope this makes sense)

dipole-dipole (or permanent dipoles): when you have two atoms covalently bonded together and one is more electronegative than the other, the more electronegative atom pulls more of the electron density towards itself, therefore that side is slightly negative and will attract the slightly positive side of another of the same molecule. so the molecules stay together.

when you have a hydrogen bonded to either nitrogen oxygen or fluorine (or ammonia) you have hydrogen bonding, then its basically the same as dipole dipole.

hope this helps

Reply 2

silentshadows

Original post by AlphaNick

almost all of which isn't on the AQA chemistry GCSE course...

Unfortunately, I can't really see a better way to explain this without going deviating slightly from the specification.

Can you think of a way explain this using only C2 knowledge?

Anyway, to expand on the previous poster's excellent help, the electron density depends on a property of all elements known as electronegativity, which is simply defined as the tendency of an element to attract electrons to itself. This depends on various factors such as atomic radius, electron shielding and nuclear attraction (if you want an example, Fluorine has very high electronegativity while Potassium and Rubidium have low electronegativity.)

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Reply 3

silentshadows

Original post by AlphaNick

You guys realise how basic GCSE chemistry is? The only tiny detail which is required for this question is that there are weak intermolecular forces due to the force of attraction between molecules which are easily overcome.

Of course, but explanations provide a much better way to learn that simply memorizing obscure pieces of information without any real understanding of why they work.

What would be the fun in learning if everyone just rigidly stuck to what was laid out and never dared to venture outside the confines of the specification?! :lol:

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Reply 4

Mattniemier

Original post by AlphaNick

Okay sure. Write out much more than you need to alongside it being irrelevant. Check the mark schemes, they won't award you for going into that much detail; let alone are they even likely to ask you anything at all on intermolecular forces.

He's trying to pass a GCSE exam, not a chemistry test. The things are different in spite of the GCSE one being labelled as 'chemistry'.

You don't need to understand anything that complicated at GCSE stage.

I agree that you don't need to write that in the GCSE exam but i find it easier to know the reason behind something rather than just that it happens. I just assumed that it was A-level as im currently doing AS AQA but last year i did the GCSE AQA. thats why i wrote such a detailed response.