Covalent Network Structures

Covalent network structures are giant 3D networks of atoms linked by covalent bonds.

Allotropes of an element have different bonding and structural patterns, and so have different physical and chemical properties

e.g. O₂ and O₃

Allotropes of Carbon

Carbon has 4 allotropes

1. Diamond

2. Graphite

3. Graphene

4. Fullerenes

Diamond

• Each carbon shares electrons with 4 other carbons

• High melting points

• Very hard

• Non-conductive

• Insoluble in H2O

• Tetrahedral

Graphite

Layered structure, sheets attract one another through L.D. forces

Each carbon bonds with 3 other carbons

Remaining electron is “spare”, can become delocalized

• High melting point

• Soft, slippery feel

• Insoluble in H₂O

• Conducts electricity

Graphene

Similar structure to graphite but single-layer only

• Conducts electricity

• Conducts heat

• Very flexible

• High melting point

Fullerene (C60)

Each carbon bonds with 3 other carbons to form a sphere.

• Semi-conductor

• Low thermal conductivity

• Low melting point

Silicon

Like carbon, silicon has 4 valence electrons

Silicon dioxide forms covalent network structures

Oxygen acts like bridge connecting silicon atoms

Physical Properties

• High melting point

• Hard

• Non-conductive

• Insoluble