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Difficulty: MediumCarbon: Allotropes, Coal Distillation, and Industrial Fuel Gases

Graphite and diamond are two crystalline allotropes of carbon that exhibit vastly different physical properties. Which of the following statements correctly accounts for why graphite conducts electricity whereas diamond is an electrical insulator?

  1. A
    Graphite consists of carbon atoms that are structurally isomeric to diamond, allowing free molecules to move through the crystal layers.
  2. Each carbon atom in graphite forms three covalent bonds using sp2sp^2 hybridization, leaving one delocalized electron per atom free to move along the hexagonal layers.Answer
  3. C
    Diamond is composed of heavier isotopes of carbon whose extra neutrons trap valence electrons within the atomic nucleus.
  4. D
    Graphite contains mobile carbon ions that dissociate under an applied electric field, whereas diamond contains neutral molecules.

Answer

Each carbon atom in graphite forms three covalent bonds using sp2sp^2 hybridization, leaving one delocalized electron per atom free to move along the hexagonal layers.
In graphite, each carbon atom forms three covalent σ\sigma-bonds via sp2sp^2 hybridization. The fourth valence electron resides in an unhybridized pp-orbital and becomes delocalized across the hexagonal layer, allowing electrical current to flow. In contrast, diamond features sp3sp^3 hybridization where all four valence electrons are tightly bound in localized covalent bonds, leaving no mobile electrons.

Step-by-Step Solution

1
Analyze the bonding and hybridization of carbon in diamond.
In diamond, each carbon atom undergoes sp3sp^3 hybridization and forms four strong covalent bonds directed tetrahedrally toward adjacent carbon atoms.
All four valence electrons per carbon atom are involved in localized single covalent bonds, leaving no free electrons to conduct electricity.
2
Analyze the bonding and hybridization of carbon in graphite.
In graphite, each carbon atom undergoes sp2sp^2 hybridization to form three strong covalent bonds within a hexagonal planar sheet.
This leaves one unhybridized pp-orbital electron per carbon atom, which forms a delocalized π\pi-electron system capable of moving freely along the layers.
3
Correlate structural features to electrical conductivity.
The presence of delocalized valence electrons in graphite enables electrical conduction, whereas the localized sp3sp^3 bonding in diamond makes it an insulator.
Electrical conduction in solid non-metallic elements requires mobile charge carriers such as delocalized electrons.

Key Concept

Structural bonding and hybridization of carbon allotropes (Graphite vs Diamond)
Estimated Time:1m 0s
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Topics

Carbon: Allotropes, Coal Distillation, and Industrial Fuel Gases

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