Specification Point 1.49:
Explain why substances with giant covalent structures are solids with high melting and boiling points

Giant Covalent Structures

Giant Covalent Structure: Contains a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds to form a giant lattice structure.

Substances with Giant Covalent Structures:

  • States: Giant covalent structures are solids.
  • Melting and Boiling point: Substances with giant covalent structures have high melting and boiling point as they have many strong covalent bonds that needs to be broken down so large amounts of heat energy is needed to overcome forces and break down bonds.

Examples of Giant Covalent Structures:

Giant covalent structures, Edexcel IGCSE Chemistry

Examples of giant covalent structures

Specification Point 1.50:
Explain how the structures of diamond, graphite and C60 fullerene influence their physical properties, including electrical conductivity and hardness

Giant Covalent Structure: Contains a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds to form a giant lattice structure.

Allotropes: Different atomic, molecular arrangements of the same element in the same physical state.

Diamond

Diamond structure, Edexcel IGCSE Chemistry

The structure of diamond – one of the allotropes of carbon

Properties:

Hard

  • Each carbon atom is joined to four other carbon atoms, forming a giant covalent structure.
  • Strong covalent bonds are difficult to break.

High Melting and Boiling Point

  • Giant Covalent Structure so there are many strong covalent bonds that needs to be broken down.
  • Large amounts of heat energy is needed to overcome forces and break down bonds.

Does not Conduct Electricity

  • All four valence (outer-shell) electrons are used in covalent bonds so there are no delocalised electrons that are mobile to conduct electricity

Uses:

  • Cutting Tools
  • Jewellery

Graphite

Graphite structure, Edexcel IGCSE Chemistry

The structure of graphite – another allotrope of carbon

Properties:

Soft and Slippery

  • Graphite is made up of two-dimensional layers of carbon atoms, which are held by weak van der Waal’s forces, lie on top of each other.
  • Forces of attraction between the layers are weak so the layers easily slide over one another and can easily be separated.

High Melting and Boiling Point

  • Within each layer, each carbon atom forms strong covalent bonds with three other carbon atoms in a giant covalent structure so there are many strong covalent bonds that needs to be broken down
  • Large amounts of heat energy is needed to overcome forces and break down bonds.

Conducts Electricity

  • Only three valence electrons are used in forming covalent bonds
  • Fourth electron is delocalised between the layers and free to move parallel to the layers to conduct an electric charge.

Uses:

  • Lubricant
  • Electrodes for Electrolysis

C60 Fullerene

The structure of C60 Fullerene

Carbon exists as graphite and diamond, but it can also form fullerenes. These are cages and tubes with different number of carbon atoms. Buckminsterfullerene is one type of fullerene. Its molecules are spherical and contain 60 carbon atoms.

Properties:

Soft

  • Each carbon atom is joined to only three other carbon atoms so there are weak intermolecular forces of attraction between molecules.
  • Intermolecular bonds can be broken down easily making it soft.

Low Melting and Boiling Point

  • Each carbon atom is joined to only three other carbon atoms.
  • This means that there are weak intermolecular forces of attraction between molecules.
  • So small amounts of heat energy is needed to overcome forces and break down bonds.

Conducts Electricity

  • Only three valence electrons are used in forming covalent bonds.
  • Fourth electron is delocalised and is free to move to conduct an electric charge.

Uses:

  • Drug Delivery System in the Body (Nanotubes)
  • Lubricant
  • Catalyst

Need help?

Aiming for a Level 9?

See if you’ve got what it takes. Test yourself with our topic questions.

Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.