CC6&7 Covalent Compounds

• A covalent bond is when a pair of electrons are shared between two atoms forming a molecule. This type of bonding normally occurs between   non-metal atoms.
• Simple covalent compound properties =

  • Low melting and boiling points (so are usually liquids or gases) 

  Due to WEAK intermolecular forces between molecules

  • CANNOT conduct electricity

  As there are no free charged particles
• Polymer= a long chain of repeating monomers.
• Monomer= a single sub-unit of a polymer.
• Longer polymers have a high melting and boiling point than shorter ones because:

  1. There are more intermolecular forces to be broken
  2. They tangle up more
• Allotrope: Same element in different structural forms
• FULLERENE:

  • Large covalent molecule
  • Each carbon atom is bonded to 3 others
  • Weak intermolecular forces 
  • Soft, slippery with a low melting point

  Little movement of free electrons so poor conductor of electricity
• GRAPHENE

  • Giant covalent structure 
  • Single layer of graphite
  • Each carbon atom is bonded to 3 others
  • Lightest known material but
  • Strong covalent bonds mean it is very strong and has a high melting point
  • Free electrons move 

  Conducts electricity
• GRAPHITE:

  • Giant covalent structure
  • Each carbon bonded to 3 others
  • High melting point
  • Weak forces between the layers
  • Layers can slide and so graphite is slippery and used as a lubricant
  • Free electrons move between layers
  • Conducts electricity

  Used as electrodes
• DIAMOND: 

  • Giant covalent structure 
  • Each carbon bonded to 4 others
  • Very strong forces between carbon atoms so hard with a high melting point
  • No free electrons
  • Does not conduct electricity 
  • Used as cutting tools in drills
• Metal Structure:

  • Regular arrangement of cations
  • surrounded by a sea of delocalised electrons
  • Strong METALLIC BONDS need a lot of energy to overcome them, so metals have a high melting point
• Metals are malleable 

  • if a large enough force is applied
  • layers of positive ions can slide over each other 

  The sea of electrons hold the ions together meaning the metal spreads out rather than breaks
• Metals conduct electricity because the delocalised electrons are free to move. If a voltage is applied, the electrons all move in the same direction and this is called a current.