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Allotropes of Carbon

World C — Carbon Chemistry

28.A — THE FOUNDATION

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R28.01 What is an Allotrope?
  • Different structural forms of the same element.
  • Identical chemical properties.
  • Dramatically different physical properties.
sp³ (3D)
sp² (2D)
R28.10 Structural Comparison
  • sp³: 4 single bonds, tetrahedral lattice (Diamond).
  • sp²: 3 bonds + 1 free electron, planar layers (Graphite/Graphene).

28.B — 3D & 2D CRYSTALS

R28.02 Diamond Structure
  • Each Carbon bonded to 4 others.
  • Rigid 3D tetrahedral network.
  • No free electrons.
R28.03 Diamond Properties
  • Hardest known natural substance.
  • High refractive index (brilliance).
  • Used in cutting tools and jewelry.
R28.04 Graphite Structure
  • Each Carbon bonded to 3 others (Hexagonal rings).
  • Forms flat 2D layers.
  • Weak Van der Waals forces between layers.
R28.05 Graphite Properties
  • Soft and slippery (layers slide over each other).
  • Excellent dry lubricant and pencil lead.
  • Good electrical conductor (4th electron is free).

28.C — ADVANCED NANOMATERIALS

R28.06 Fullerenes (C60)
  • Buckminsterfullerene.
  • Hollow soccer-ball shape (Truncated icosahedron).
  • Contains 20 hexagons and 12 pentagons.
  • Potential in drug delivery systems.
R28.07 Graphene
  • A single, one-atom-thick layer of graphite.
  • 200x stronger than steel.
  • Incredible electrical and thermal conductivity.
  • The "wonder material" of the 21st century.
R28.08 Carbon Nanotubes
  • Graphene sheet rolled into a seamless cylinder.
  • Single-walled (SWCNT) or Multi-walled (MWCNT).
  • Exceptional tensile strength and conductivity.

28.D — AMORPHOUS & COMPARISONS

R28.09 Amorphous Carbon
  • No definite crystalline structure.
  • Coal, Coke, Charcoal, Lampblack.
  • Used primarily as fuels and reducing agents.
vs
R28.11 Conductivity Differences
  • Diamond: Insulator. All 4 valence e⁻ locked in covalent bonds.
  • Graphite/Graphene: Conductors. 1 delocalized e⁻ per carbon atom flows freely along the plane.
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R28.12 Thermal Properties
  • Diamond is the best known thermal conductor.
  • Heat transfers via stiff lattice vibrations (phonons), not electrons.
  • Used as heat sinks in high-end electronics.