1. Forms of Carbon

2. Diamond Covalent crystals: C, Si, Ge, SiC Strong sp 3  bonds form tetrahedral structure Face Centered Cubic lattice (fcc) –8 C atoms at the vertices of the cube, 6 C atoms in the face center, and 4 more within the unit cell –Each C is tetrahedrally bonded to four others –All C-C bonds 1.54 Ǻ Properties –Extremely hard Strong rigid structure (macromolecule) –Insulator No delocalized e – (  bonds) –High index of refraction and strong dispersion of light Diamond film (CVD)

3. Diamond

4. Graphite Parallel sheets of graphene –Hexagonal, aromatic, “benzene” ring arrays –sp 2  bonds stronger than in diamond Delocalized  e – between sheets –Covalent-metal bond Van der Walls forces between sheets Randomly oriented graphite grains Properties –Anisotropic –Electrical conductivity along sheets Graphene: zero gap semi-conductor –Soft, greasy and lubricating –Strong absorption of light On  e –

5. Graphite

6. Fullerene Richard Buckminster Fuller (1895 - 1993) Bulk solid state: Fullerite Closed cage C molecule Pentagons in hexagonal structure –Isolated Pentagon Rule IPR (stress) –Spheroidal curvature –Admixture of sp 3 hybridization C 60 –Diameter 7 Ǻ With  e 10 Ǻ, cavity 4 Ǻ –Hexagons (20) Single bonds (red) 1.40 Ǻ Double bonds (yellow) 1.46 Ǻ –Pentagons (12) Single –Delocalized  e – Mostly outside the cage Higher density on double bonds –Influence of sp 3 and curvature Decreases with increasing n in C n

7. Nanotube Cylindrical C nanostructure –Graphene sheets wrapped into a cylinder Armchair (1), zigzag (2), chiral (3) –sometimes capped by fullerene-like structure –Diameter: 1 to several nm –Length: 10 1  m Single-walled carbon nanotubes SWCNT –Bundles (ropes) of tens SWCNT stuck in triangular lattice Multi-walled carbon nanotubes MWCNT –Few to few tens of concentric cylinders Spacing close to graphite 3.35 Ǻ Toughest materials ever known –High elastic modulus of graphene sheets 1 2 3

8. Forms of Carbon sp 2 pure sp 2 pure sp 3