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This paper states that the carbon atoms in a sheet of graphene form 3 $\sigma$ bonds with the neighbouring carbons and a $\pi$ bond that comes out of the plane (in the $z$ direction).

Unfortunately the paper doesn't go into detail about what this $\pi$ bond is exactly. I thought it could be a lone pair but carbon can't do that with 3 $\sigma$ bonds already in place.

What is the bond bonding the carbon to? How is this $\pi$ bond possible?

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  • $\begingroup$ There's an extra electron left from each carbon that it shares with the carbon below it. Btw, the configuration is not very stable and thus graphene layers can slide. $\endgroup$
    – Yuzuriha Inori
    Commented Mar 11, 2018 at 16:44
  • $\begingroup$ Graphene is like a sheet of aromatic rings (aromatic as in the benzene molecule). $\endgroup$
    – user137289
    Commented Mar 11, 2018 at 17:11
  • $\begingroup$ @YuzurihaInori So if it only shares with one other carbon, does that mean that there has to be an even number of carbons? $\endgroup$
    – Niamh O'SS
    Commented Mar 11, 2018 at 18:32

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I want to answer my own question as I now understand how the $\pi$ bond forms.

As @YuzurihaInori said;

There's an extra electron left from each carbon that is shares with the carbon below it.

This image is what helped my understanding of it pi bonds

The $\pi$ orbitals form together to make the "$\pi$-bands" the paper was talking about. It also helped me to understand why graphene is such a good conductor: due to delocalised electrons in the $\pi$ orbitals.

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