Covalent bonding

• Covalent bonding - a bond formed when non-metals share electrons
• Giant covalent structure - a structure with many atoms joined to each other by lots of strong, covalent bonds giving a high melting point and poor electrical conductivity (except graphite)
• Simple molecular substances have:

  • strong covalent bonds
  • weak intermolecular forces
• Properties of simple molecular substances:

  • Low melting and boiling point
  • Don't conduct electricity
• Polymers - large molecules made up of many monomers joined together by covalent bonds
• Polymers are usually solid at room temperature because they have strong intermolecular forces
• Properties of giant covalent structures:

  • High melting and boiling point
  • Don't conduct electricity
• Carbon allotropes:

  • Diamond
  • Graphite
  • Graphene
  • Fullerenes
  • Nanotubes
• Diamond:

  • Each carbon atom forms 4 covalent bonds
  • Very hard
  • High melting and boiling point
  • Doesn't conduct electricity
• Graphite:

  • Each carbon atom forms 3 covalent bonds but no bonds between layers
  • Soft and slippery
  • High melting and boiling point
  • Conducts electricity and thermal energy
• Graphene:

  • Each carbon atom forms 3 covalent bonds
  • Strong and light
  • High melting and boiling point
  • Conducts electricity
• Fullerenes - hexagonal rings of carbon atoms, which contain 5-7 carbon atoms, creating hollow shapes
• Thermosoftening polymers - a type of polymer which soften/melt when heated.

  As there are no bonds between polymer chains. They have strong intermolecular forces which ensure that they are solid at room temperature. But they are overcome when heated.