[Clairenoel28]

Hello everyone,

I am a little bit confused because I do not quite understand why each carbon atom in graphite has a delocalised electron, which gives its property of conducting electricity. In graphite, carbon forms one double bond and two single bonds as it is sp2 hybridised, so how does it have one spare electron if all of them are bonded?

Thank you

[Hunter2]

The double bond Pi-electrons give the conductivity. The molecule looks like of thousands benzene rings condensed together. So double bond and single bond can switch back an forward.

[mikasaur]

In graphite, carbon forms one double bond and two single bonds as it is sp2 hybridised

I think here is where you're mental model isn't quite right.

Each C has sp² hybridization, which means that the s, p_z, and p_x orbitals hybridize and form 3 σ-bonds with its three neighbors. This leaves an e^- in the un-hybridized p_y orbital of each C atom. The p_y orbital is perpendicular to the plane of the σ bonds (see the figure on the right) and forms π bonds between the C atoms. These pi bonds give rise to delocalized electrons; they're free to travel along the plane of the C rings.

[Enthalpy]

And a third version of the same:

Benzene and graphite have no single and double bonds. They are "aromatic" compounds where electrons spread over many atoms, in this case the whole compound's carbon skeleton.

The same happens with "conjugated" dienes and bigger compounds that are often represented with double bonds alternating with single ones but where electrons spread over many atoms.

Similar things happen with "resonances".

Though, electricity conduction isn't exactly the same as delocalized electrons. It relates more with the compound offering the electrons a set of possible states whose energy is near enough to an other, so that some electrons can change their state by a limited amount of energy, and move.

If willing to go deeper, maybe the idea of "bond" between two atoms must be given up at that point. This idea is fantastically useful in chemistry, hence must be learned and used, but is known to be wrong. For instance silicon and diamond crystals would have only single bonds, but their proper model for electrical and optical properties tells that each valence electron spreads all over the crystal, and conductivity relates with valence and conduction bands being full or not.

[Clairenoel28]

Thanks this helped me, I thought that Carbon in graphite makes double bonds but it only produces 3 single bonds. This is where the delocalised electron comes in