Covalent Bonding

• Covalent bonds are formed by non-metal atoms sharing electrons.
• Describe the structure and bonding of a giant covalent substance:

  Billions of atoms bonded together by strong covalent bonds.
• Describe the structure and bonding of small molecules:

  Small numbers of atoms group together into molecules with strong covalent bonds between the atoms and weak intermolecular forces between the molecules.
• Describe the structure and bonding of polymers:

  Many identical molecules joined together by strong covalent bonds in a long chain, with weak intermolecular forces between the chains.
• Giant covalent substances have high melting points because it takes a lot of energy to break the strong covalent bonds between the atoms.
• Small covalent molecules have low melting points because a small amount of energy is needed to break the weak intermolecular forces.
• Large molecules have higher melting points than small molecules because the intermolecular forces are stronger in large molecules.
• Most covalent substances do not conduct electricity because they do not have delocalised electrons or ions.
• Describe the structure and bonding in graphite:

  Each carbon atom is bonded to three others in hexagonal rings arranged in layers - it has delocalised electrons and weak forces between layers.
• Graphite can conduct electricity because the delocalised electrons can move through the graphite.
• Graphite is soft because the layers are not bonded so they can slide over each other.
• Graphene is a single layer of graphite.
• Graphene is strong and it can conduct electricity.
• A fullerene is a hollow cage of carbon atoms arranged as a sphere or a tube.
• A nanotube is a hollow cylinder of carbon atoms.
• Nanotubes have high tensile strength and they can conduct electricity.
• Uses of fullerenes:

  • Lubricants
  • Drug delivery (spheres)
  • High-tech electronics