(b) Carbon
Graphite, diamond, fullerene, and amorphous carbon are carbon allotropes.
Usually a carbon atom forms four bonds using four valence electrons.
Graphite Graphite is structured as layers of honeycomb-shaped 6 membered rings of
carbon atoms that look like condensed benzene rings without any hydrogen atoms (Fig.
4.4). The carbon-carbon distance between in-layer carbon atoms is 142 pm and the bonds
have double bond character analogous to aromatic compounds. Since the distance
between layers is 335 pm and the layers are held together by comparatively weak van der
Waals forces, they slide when subjected to an applied force. This is the origin of the
lubricating properties of graphite. Various molecules, such as alkali metals, halogens,
metal halides, and organic compounds intercalate between the layers and form
intercalation compounds. Graphite has semi-metallic electrical conductivity (about 10-3
Ωcm parallel to layers and about 100 times more resistant in the perpendicular direction).