7.3 Periodic trends in bonding and structure

• Metals have a giant metallic lattice structure held together by metallic bonds
• Metallic bonding

  • each metal atom forms a positive ion
  • positive ions arranged into a regular lattice
  • outer shell electrons are delocalised
• Delocalised electrons are free to move, so can carry charge and heat
• A metallic bond is a strong electrostatic attraction between positive ions and delocalised electrons
• In Periods 2 and 3, boron, carbon and silicon form giant covalent lattices
• Large amount of energy is needed to break covalent bonds
• Carbon can form different lattices = diamond, graphite and graphene
• Diamond contains carbon atoms each forming 4 covalent bonds
• Graphite contains carbon atoms with 3 covalent bonds and one delocalised electron per atom
• Graphene is a layer of graphite
• Diamond can't conduct electricity because there are no mobile charge carriers
• Graphite and graphene can conduct electricity because the delocalised electrons are free to move and carry charge
• Simple molecules only have induced dipole-dipole interactions and therefore have lower melting/boiling points