Giant Covalent and Simple Molecular

Van der waal's forces occur between non-polar,simple covalent molecules. They are caused by the uneven distribution of electrons, which induces an instantaneous dipole in the molecule. This then induced dipoles in neighbouring molecules. The electrostatic attraction between these dipoles is the van der waal's force but they are extremely weak compared to all other types of bonding, so not much energy is needed to overcome them.


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Van der waal's forces occur between non-polar,simple covalent molecules. They are caused by the uneven distribution of electrons, which induces an instantaneous dipole in the molecule. This then induced dipoles in neighbouring molecules. The electrostatic attraction between these dipoles is the van der waal's force but they are extremely weak compared to all other types of bonding, so not much energy is needed to overcome them.


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They are only extremely weak in very small molecules. In larger molecules, such as polymers they are strong. In sulphur, phosphorus and iodine they are strong enough to make the structures solid at room temperature. This makes them stronger than the hydrogen bonding in water!

Okay, so my spec doesn't cover van der waals, (or we just haven't done it yet) but any small molecule that's covalently bonded will me simple molecular. Iodine chloride can't be a network as both I and Cl can only make one covalent bond to get a full outer shell. (Grp7) Carbon and silicon can form 4 bonds, so they are able to make giant networks. Silicon oxide is a network as silicon can bond to 4 oxygens, and each oxygen can bond to 2 silicon atoms. Diamond and graphite are made of only carbon, so they can easily form a network, the difference is the way the carbons are arranged. I have attached some photos, I hope that helps.

As for id id, pd-pd and hydrogen bonds:
Pretty much every molecule can form id-is bonds. The electrons are constantly moving around the molecule, so at a specific instant, there will be more electrons on one end of the molecule than the other. This creates a dipole, but only for that instant.

Pd-pd bonds are between molecules with a dipole charge, eg HCl. Chlorine is a lot more electronegative than hydrogen, so it attracts the shared electrons more.

Here's how we were taught hydrogen bonding:
You need 2 things:
1) a Hydrogen atom attached to a FON (flourine/oxygen/nitrogen) on one molecule.
2) a lone pair on the FON in the other molecule.
So for example in water, there is a hydrogen attached to an oxygen (1) and it hydrogen bonds to the lone pair on the FON (in this case oxygen) on another water molecule. So H2O can hydrogen bond.

I hope this has helped you, if you need anymore help just let me know


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Van der waal's forces occur between non-polar,simple covalent molecules. They are caused by the uneven distribution of electrons, which induces an instantaneous dipole in the molecule. This then induced dipoles in neighbouring molecules. The electrostatic attraction between these dipoles is the van der waal's force but they are extremely weak compared to all other types of bonding, so not much energy is needed to overcome them.


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They are only extremely weak in very small molecules. In larger molecules, such as polymers they are strong. In sulphur, phosphorus and iodine they are strong enough to make the structures solid at room temperature. This makes them stronger than the hydrogen bonding in water!

You've all helped me, particularly BarneyMersich, so thank you! Just to clarify:

1. Giant covalent structures are normally group 4 and are dependent on the number of bonds.
2. Simple covalent structures are normally group 7/6/5 and again, depends on the number of bonds. There are Van der Waal bonds between molecules and in larger molecules, the higher number of electrons makes stronger VDW bonds which can make structures solid at RTP and can be stronger than H-bonding in water. So is this VDW the bonding in Iodine crystals etc?
3. Dipole - dipole bonds are caused when there is a dipole in one molecule. A dipole in one molecule is because of difference in electronegativities of atoms. Another question - how do you know whether the atoms have a big enough difference in electronegativity to make a molecule polar? I can't really learn electronegativities of all the atoms and if you could give me the most common atoms that come up together with their electronegativities, or how you recognise if there is a dipole in a molecule, that would be great! And does this bare any similarity to ionic bonding. How can I stop getting them confused i.e. is Dipole-dipole bonding only between non-metals, including hydrogen?
4. Hydrogen bonding is between two molecules, one with H-O, H-N, H-F only and the other with the FON - H and a lone pair.

Can any of you please answer the above questions? Thank you again for the help everyone. I think I'm beginning to get it.

You've all helped me, particularly BarneyMersich, so thank you! Just to clarify:

1. Giant covalent structures are normally group 4 and are dependent on the number of bonds.
2. Simple covalent structures are normally group 7/6/5 and again, depends on the number of bonds. There are Van der Waal bonds between molecules and in larger molecules, the higher number of electrons makes stronger VDW bonds which can make structures solid at RTP and can be stronger than H-bonding in water. So is this VDW the bonding in Iodine crystals etc?
3. Dipole - dipole bonds are caused when there is a dipole in one molecule. A dipole in one molecule is because of difference in electronegativities of atoms. Another question - how do you know whether the atoms have a big enough difference in electronegativity to make a molecule polar? I can't really learn electronegativities of all the atoms and if you could give me the most common atoms that come up together with their electronegativities, or how you recognise if there is a dipole in a molecule, that would be great! And does this bare any similarity to ionic bonding. How can I stop getting them confused i.e. is Dipole-dipole bonding only between non-metals, including hydrogen?
4. Hydrogen bonding is between two molecules, one with H-O, H-N, H-F only and the other with the FON - H and a lone pair.

Can any of you please answer the above questions? Thank you again for the help everyone. I think I'm beginning to get it.

They are only extremely weak in very small molecules. In larger molecules, such as polymers they are strong. In sulphur, phosphorus and iodine they are strong enough to make the structures solid at room temperature. This makes them stronger than the hydrogen bonding in water!

Okay, so, as I said I didn't know what Van Der Waal was, I know realise I was slightly incorrect. Whenever you see write Van Der Waals, I mean instantaneous dipole induced dipole. Sorry about that!


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Sometimes also called "London Dispersion Forces".

3 names for the same thing!

So is Van Der Waals id-id, or is it a collective for id-id & pd-pd ?


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Just id-id, not pd-pd.

Hmm, double checking there is some controversy on that one.

Most A-level specifications describe VDW and dp-dp as different, however id-id and pd-pd both come under the category of VDW.

So for the sake of the exam, they are different.

Ah great so I was correct the first time thanks haha


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So:
1) yeah that sounds about right, as long as you remember diamond, graphite and silicon dioxide, you should be fine, at least that's on out spec (OCR salters B)

2) simple molecular doesn't really depend on number of bonds: as long as it isn't a network but it's covalent it will me simple molecular. As long as you can look at something like water, and realise that all the bonds are used up, so it can't be a network you should be okay.
Also,
Careful with wording:

"in larger molecules, the higher number of electrons makes stronger VDW bonds"

I know what you meant, but the mark schemes (especially on my exam board / exam) are very strict on wording. In larger molecules the higher number of electrons causes the molecule to make stronger VDW bonds with adjacent molecules. the way you wrote it suggested the electrons are doing the bonding. Rememer, these are intermolecular, so thats bonds between molecules, as opposed to intramolecular, which are bonds within a molecule (covalent etc).

3) dipole dipoles are when there's a dipole in both molecules.
As for electronegativity:
The general rule of thumb is the top right side of the periodic table is the most electronegative, the bottom left is the least. Things like H-Cl are polar, as Cl is very electronegative and H is not. (Joke: how are bonds like bears? Some are polar, some are not)
This is nothing like ionic bonding. These are due to bonds in molecules having a dipole. A dipole is only a small charge, usually written as δ- and δ+ (that's a delta) this is caused by the shared electrons being closer to one atom than the other (the more electronegative one)
ionic bonding is where there is a charge due to loss or gain of electrons. In an atom, and there are no shared electrons. In fact, the two atoms/molecules ionically bonded are only 'as one' when in solid crystal form. When dissolved in water they split into the ions.

4) yes that's right, but the second one doesn't necessarily need a Hydrogen I don't think: a hydrogen attached to a FON, can hydrogen bond to the lone pairs on another FON.

That's quite an essay, I may have missed something. Anything you're still unsure about just post!


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1. Yes. But polymers are also giant covalent structures made up of simple monomer repeating units. If you still haven't covered polymers then don't worry. It would also be better to go through the specs of your relevant exam board. Mostly they'll list all the giant covalent structures that students would be assumed to know at the exam.
2. Yes and yes. Also remember that vanderwall is a general term that covers both instantaneous dipole - induced dipole intermolecular bonds (also called London forces or dispersion forces) and permanent dipole permanent dipole bonds so in the exam it's better to specify what of the two is present. My teacher advises us to use the VDW term only if both are present. Yes instantaneous dipole induce dipole bonds are present in iodine and not pds. Hope you understand why.
3. Leave aside metals and metallic ions in organic chemistry. With a bit of experience it's easy to identify a significant polar bond. Remember that alkane and alkene chains do not have polar bonds on their own (significant polar bonds ).
A molecule is polar if it fulfils two conditions. a It has at least one polar bond. b it is asymmetrical in the sense that the centre of positive and negative charge don't coincide and cancel each other. So chloromethane is polar but tetrachloromethane is not.
BUT a molecule dies not need to be polar to have pdpd forces between them as only polar bonds are needed. So both the above mentioned molecules may show pdpd forces of attraction between each other.
4. Yes. It's between an highly electropositive hydrogen atom and an highly electronegatuve atom. Those are the only possibilities.

In chemistry it's important to ask yourself why you are studying something.

The study of intermolecular bonds is important to explain differences in melting and boiling temperatures of organic substances. Hydrogen bonds are the strongest generally and the more the number of these bonds the higher the value. Also remember that one with fluorine is stronger than one with oxygen which is stronger than one nitrogen. Hope you understand why. Then comes permanent dipole bonds and it's number and strenght.
Then comes induced dipole instantaneous dipole which depends on the number of electrons and surface area (if same number of electrons like in structural isomers)
It's also important to explain solubilities. Like dissolves in like concept may explain why polar substances dissolve in each other and nonpolar dissolves in each other, but is a simplification. When you learn about the properties of different homologous series it'll be more clearer.


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Hmm, double checking there is some controversy on that one.

Most A-level specifications describe VDW and dp-dp as different, however id-id and pd-pd both come under the category of VDW.

So for the sake of the exam, they are different.

x

I got confused with ionic because I thought they were similar but now I realise polar covalent bonds are INTRAmolecular forces (which are on the scale between pure ionic and pure covalent.

Hydrogen bonding is between two molecules, one with H-O, H-N, H-F only and the other molecule with the FON - H and a lone pair. Hydrogen bond occurs between the δ- atom of one molecule (draw it to lone pairs if there) and δ+ atom of the other molecule.