C-C bonds Miracle ?!?!?!

[chuinhen]

Why is c-c bond in graphite is stronger than c-c bond in diamond ??

[Neil9327]

I think you didn't mean to say what you did. Let's rephrase your question (Let me know if this is wrong)

 

"Why is the C-C bond weaker in Graphite than it is in diamond"

 

Well the answer is that the actual C-C bond is the same strength in both materials, and is as strong as diamond. But in graphite the carbon forms layers and these layers are connected with other layers by only a very weak force, and they can shear apart very easily. Whereas in diamond the carbon atoms are held together in a three-dimentional lattice (christal) structure which is strong in all directions, so no shearing can easily occur

[insane_alien]

the C-C bond in graphite(not the one between the layers) is kind of like the C-C bonds in benzene because there are delocalised electrons involved and each carbon only has 3 bonds. this is also what allows it to conduct. nothing miraculous about it.

 

Edit since neil went ninja on my post: the C-C bonds in graphite are actualy stronger than those in diamond because they have some double bond character. although the bonds between layers are incredibly weak. in a diamond however all the bonds are your average sigma bonds. hence it doesn't conduct. and the lattice structure also gives it an appearence of stregnth.

[Tartaglia]

The bonds in diamond are the classic sp3 sigma bonds and so the bond order is precisely 1

The bonds in graphite are sp2 type bonds with a delocalised pi system across layers. Since the bonds between layers are merely van der waals the average bond order in graphite is 1.333333. Thus within layers they are stronger than diamond (but weaker than benzene which has bond order 1.5).

[Neil9327]

I don't know what you mean by going ninja on my post. But yes I did edit it after posting it for some reason I can't remember. But I didn't see your post, they both arrived at the same time!

 

Thanks for the double bond clarification. didn't know that.

 

Does that mean that if you produce perfectly layered graphite that it will be a conductor in one direction, but an insulator in the other?

[Tartaglia]

If you have a single crystal of graphite then the anisotropic conductivity can be observed, with conduction within layers and insulation between layers

[woelen]

You can also nicely see this with plain pencils. The soft ones of mainly layers of graphite, which are in parallel to the paper, when you are drawing. So, when drawing, the "sheets" of graphits easily slip away from the tip of the pencil.

 

The hard pencils mainly have "sheets" along the long direction of the rod inside. These are harder, because now, sheets have to break apart. These hard pencils have a much better conductivity along the long direction of the thin rod.