AQA GCSE FOUNDATION Chemistry: Giant Covalent Structures

Giant Covalent Structures: Diamond, Graphite, and Silicon Dioxide

Giant covalent structures are formed when atoms bond together in a continuous network, creating a large, three-dimensional structure. These structures are strong and have high melting points due to the many strong covalent bonds present.

Diamond

• Structure: Carbon atoms form four strong covalent bonds in a tetrahedral arrangement. This creates a rigid, three-dimensional structure with no free electrons.
• Properties:
  • Extremely hard: Diamond is the hardest naturally occurring substance due to the strong covalent bonds.
  • High melting point: A lot of energy is required to break the numerous strong covalent bonds.
  • Does not conduct electricity: Diamond has no free electrons to carry an electrical current.
  • Insoluble in water: Covalent bonds are strong and not easily broken by water molecules.

Graphite

• Structure: Carbon atoms form three strong covalent bonds, creating layers of hexagonal rings. These layers are held together by weak intermolecular forces (Van der Waals forces).
• Properties:
  • Soft and slippery: The layers can easily slide over each other due to the weak intermolecular forces.
  • High melting point: Within the layers, the strong covalent bonds require a lot of energy to break.
  • Good conductor of electricity: Each carbon atom has one free electron which can move between the layers, allowing for electrical conductivity.
  • Used as a lubricant: Its slipperiness makes it ideal for use as a lubricant.

Silicon Dioxide (SiO2)

• Structure: Silicon atoms form four strong covalent bonds with oxygen atoms, creating a giant network structure similar to diamond.
• Properties:
  • Hard and strong: The strong covalent bonds contribute to its hardness.
  • High melting point: A lot of energy is needed to break the numerous covalent bonds.
  • Does not conduct electricity: Silicon dioxide has no free electrons to carry an electrical current.
  • Found in sand and quartz: It is a common compound found in nature.

Summary Table

Applications

• Diamond: Jewelry, cutting tools, drilling bits
• Graphite: Pencil lead, lubricants, electrodes in batteries
• Silicon Dioxide: Glass, sand, computer chips