covalent bonding

• Particle model


  The three states of matter can be represented in the particle model
• Covalent bonding


  Atoms share pairs of electrons to form strong chemical bonds
• Covalent bond


  A covalent bond is formed between non-metals when they share electrons
• Number of electrons shared

  Depends on how many extra electrons an atom needs to make its outer shell full
• Particle model assumptions


  • There are spaces between the particles
  • All particles in a substance are spherical
  • The spheres are solid
• Energy needed to change state

  Depends on the forces between the particles, stronger forces mean higher melting/boiling point
• Covalent structures


  • Single bond each atom shares one pair of electrons
  • Double bond each atom shares two pairs of electrons
• Types of covalent structures

  • Giant covalent
  • Small molecules
  • Large molecules
• Giant covalent


  • Has billions of atoms, each one with a strong covalent bond to a number of others
  • Example: diamond
• Small molecules


  • Each molecule contains only a few atoms with strong covalent bonds between them
  • Held together by weak intermolecular forces
  • Example: water
• Large molecules


  • Many repeating units joined by covalent bonds to form a chain
  • Separate chains held together by stronger intermolecular forces than small molecules
• Polymers


  Examples of large molecules
• Graphite


  • Made of carbon atoms bonded in hexagonal rings in layers
  • Each carbon atom has one spare electron that is delocalised and can move through the structure
  • Layers can slide over each other so graphite is softer than diamond
• Delocalised electrons


  Free to move around the structure, allowing graphite to conduct electricity
• Fullerenes


  • Spheres of carbon atoms arranged in rings to form hollow shapes
  • Can be used as lubricants and for drug delivery
• Nanotubes


  • Carbon atoms arranged in cylindrical tubes
  • Have high tensile strength, useful in electronics
• Graphene


  Single layer of graphite, strong and can conduct electricity, used in composites and touch electronics