11.1 Carbon Fullerenes

Carbon, with atomic number 6 and a ground state electronic configuration 1 s ² 2 s ² 2 p ⁶, is the most versatile element of the Periodic Table. It gives origin to Organic Chemistry. The most stable solid form of pure carbon is graphite, formed by planar carbon layers bound to the neighbor layers by weak Van der Waals forces. So the layers can be exfoliated easily. On the other hand the binding of the carbon atoms within a layer is very strong. The atoms form a honeycomb-like two-dimensional lattice. In this lattice the electrons of the carbon atoms form sp ² hybrid orbitals that interact strongly with the three neighbor atoms leading to the formation of localized strong ? bonds at angles of 120 and delocalized weak ? bonds. Another form of carbon, of interest in solid state physics, is diamond. In this case the formation of sp ³ hybrid orbitals leads to tetrahedral coordination around each atom. In spite of the weak interlayer binding energy of graphite, this is the most stable form of carbon, that is, the phase with the highest binding energy.