Which of the following carbon allotropes is/are good conductor(s) of electricity ? 1. Diamond 2. Graphite 3. Fullerene Select the correct answer using the code given below :
2 only
Understanding Electrical Conductivity in Carbon Allotropes
Electrical conductivity is the ability of a material to allow electric current to pass through it. This ability depends on the presence of free or delocalized electrons or ions within the material that can move when an electric field is applied. We will examine the structures and bonding in the given carbon allotropes to determine their conductivity.
Analysis of Carbon Allotropes and Conductivity
1. Diamond
Diamond is a well-known allotrope of carbon. Let's look at its structure and properties:
- Structure: In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This forms a rigid, three-dimensional network structure.
- Bonding: Every valence electron of each carbon atom is involved in forming these strong covalent bonds. The carbon atoms are sp<sup>3</sup> hybridized.
- Free Electrons: Due to all valence electrons being tightly held in covalent bonds, there are no free or delocalized electrons available to carry electric charge.
- Conductivity: Therefore, diamond is an excellent electrical insulator (poor conductor).
2. Graphite
Graphite is another common allotrope of carbon. Let's examine its structure and properties:
- Structure: In graphite, carbon atoms are arranged in layers of hexagonal rings. Within each layer, each carbon atom is covalently bonded to three other carbon atoms. The layers are stacked on top of each other and held together by weak Van der Waals forces.
- Bonding: Each carbon atom within a layer is sp<sup>2</sup> hybridized, forming three strong covalent bonds with neighboring carbon atoms in the same plane. The fourth valence electron on each carbon atom is not involved in these planar covalent bonds.
- Free Electrons: The remaining fourth valence electron on each carbon atom is delocalized across the entire layer, forming a pi (\(\pi\)) electron cloud. These delocalized electrons are relatively free to move within the layers.
- Conductivity: The presence of these mobile delocalized electrons makes graphite a good conductor of electricity, particularly along the layers.
3. Fullerene
Fullerenes, such as Buckminsterfullerene (C<sub>60</sub>), are cage-like structures made entirely of carbon atoms.
- Structure: Fullerenes typically consist of carbon atoms arranged in pentagonal and hexagonal rings that form a closed shell, like a hollow sphere or ellipsoid.
- Bonding: Carbon atoms in fullerenes are predominantly sp<sup>2</sup> hybridized, similar to graphite. They have a system of delocalized pi (\(\pi\)) electrons.
- Conductivity: Pure fullerenes are generally semiconductors or insulators, although their conductivity can be enhanced by doping them with alkali metals or other substances, turning them into conductors or even superconductors at low temperatures. However, in their standard, undoped form, they are not considered good conductors compared to graphite.
Comparing Conductivity: Diamond, Graphite, Fullerene
Based on the analysis:
- Diamond: Poor conductor (insulator)
- Graphite: Good conductor
- Fullerene (pure): Semiconductor/Insulator
The question asks which is/are good conductor(s) of electricity. Among the options listed, only Graphite is consistently described as a good conductor due to its delocalized pi electrons.
Conclusion
Considering the electrical properties of Diamond, Graphite, and Fullerene, only Graphite is a good conductor of electricity in its standard form. Diamond is an insulator, and Fullerene is typically a semiconductor or insulator.
Therefore, the correct answer is the one that includes only Graphite (2).
| Carbon Allotrope | Structure & Bonding | Presence of Free Electrons | Electrical Conductivity |
|---|---|---|---|
| Diamond | Tetrahedral network (sp<sup>3</sup>) | None | Poor (Insulator) |
| Graphite | Layered hexagonal (sp<sup>2</sup>) | Delocalized pi (\(\pi\)) electrons within layers | Good (within layers) |
| Fullerene | Spherical cage (sp<sup>2</sup>) | Delocalized pi (\(\pi\)) electrons | Semiconductor/Insulator (Pure) |
Revision Table: Properties of Carbon Allotropes
| Property | Diamond | Graphite | Fullerene (C<sub>60</sub>) |
|---|---|---|---|
| Hardness | Very Hardest known natural material | Soft, slippery | Moderately Hard |
| Electrical Conductivity | Poor (Insulator) | Good (along layers) | Semiconductor/Insulator (Pure) |
| Thermal Conductivity | Very High | High (along layers), Low (across layers) | Low |
| Structure | 3D network | Layered structure | Spherical cage |
| Hybridization | sp<sup>3</sup> | sp<sup>2</sup> | sp<sup>2</sup> |
Additional Information on Carbon Allotropes and Conductivity
The difference in electrical conductivity among carbon allotropes highlights how the arrangement and bonding of the same element's atoms can drastically change its physical and chemical properties. The presence of delocalized electrons is a critical factor for good electrical conductivity in materials.
- Other carbon allotropes exist, such as carbon nanotubes and graphene. Graphene, a single layer of graphite, is an excellent electrical conductor due to its 2D structure with delocalized electrons.
- Carbon nanotubes, which can be thought of as rolled-up sheets of graphene, can be metallic (good conductors) or semiconducting depending on their structure (chirality).
- The weak forces between graphite layers allow them to slide past each other, making graphite soft and useful as a lubricant, unlike hard diamond.
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