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Forms of Carbon

Forms of Carbon. Diamond. Covalent crystals: C, Si, Ge, SiC Strong sp 3 s 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

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Forms of Carbon

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  1. Forms of Carbon

  2. Diamond • Covalent crystals: C, Si, Ge, SiC • Strong sp3s 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– (p 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 • sp2s bonds stronger than in diamond • Delocalized p 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 p 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 sp3 hybridization • C60 • Diameter 7 Ǻ • With e 10Ǻ, cavity 4Ǻ • Hexagons (20) • Single bonds (red) 1.40 Ǻ • Double bonds (yellow) 1.46 Ǻ • Pentagons (12) • Single • Delocalized p e– • Mostly outside the cage • Higher density on double bonds • Influence of sp3 and curvature • Decreases with increasing n in Cn

  7. 1 2 3 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: 101mm • 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

  8. sp2 sp2 pure sp2 pure sp3 Forms of Carbon

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