S2.2.7 Covalent network structures Notes

Carbon Allotropes and Properties of Covalent Networks

Diamond: A Three-Dimensional Giant Covalent Network

1. In diamond, each carbon atom is covalently bonded to four others in a tetrahedral arrangement, forming a three-dimensional lattice.
2. This rigid structure is what makes diamond incredibly hard.
3. Bonding: Each carbon atom forms four strong covalent bonds.
4. Geometry: Tetrahedral, with bond angles of approximately $109.5^\circ$.
5. Key Properties:
   1. Hardness: Diamond is the hardest naturally occurring material, making it ideal for cutting tools and abrasives.
   2. Electrical Conductivity: Poor conductor because all electrons are localized in covalent bonds.
   3. Thermal Conductivity: Excellent thermal conductor due to its strong lattice structure.

Graphite: Layers of Hexagonal Sheets

1. Graphite consists of layers of carbon atoms arranged in hexagonal rings.
2. Each carbon atom is covalently bonded to three others, leaving one delocalized electron per atom.
3. Bonding:
   1. Strong covalent bonds within layers.
   2. Weak London dispersion forces between layers.
4. Geometry: Trigonal planar, with bond angles of $120^\circ$.
5. Key Properties:
   1. Electrical Conductivity: Good conductor due to delocalized electrons that can move freely within layers.
   2. Lubrication: Layers slide over one another, making graphite an effective lubricant.
   3. Softness: Weak interlayer forces allow layers to flake off, which is why graphite is used in pencils.

Graphene: A Single Layer of Graphite

1. Graphene is a single, one-atom-thick sheet of carbon atoms arranged in a hexagonal lattice.
2. It is essentially an isolated layer of graphite, but its properties are extraordinary.
3. Bonding: Each carbon atom forms three covalent bonds, with delocalized electrons across the sheet.
4. Geometry: Trigonal planar, with bond angles of $120^\circ$.
5. Key Properties: