Topic 2 - Bonding

• Bonding:

  • Metallic Bonding - Metals
  • Ionic bonding - Metals and non-metals
  • Covalent - Non-metals
• Metallic bonding forms a lattice of ions surrounded by a sea of delocalised electrons. They are free to move - making metals good conductors of electricity and heat.
• Metals atoms donate electrons to non-metals to form ions
• The charges of all ions in an ionic compound must add up to zero
• Ions are arranged in a lattice of repeating units of positive and negative ions forming a crystal
• Ionic substances have high melting and boiling points due to strong ionic bonds as the ions have strong electrostatic forces between them
• Ions can conduct electricity when molten or in solution as the ions are free to move in those states and they carry charge
• Ionic compounds are also called salts
• Positive ions are cations
• Negative ions are anions
• In covalent bonding, atoms share electrons for a full outer shell
• Simple covalent structures are molecules with a small number of atoms
• Simple covalent structures have low boiling points due to the weak intermolecular forces
• Giant covalent structures consist of repeating units of atoms to make giant molecules e.g diamond
• Giant covalent structures have a very high melting point due to the amount of covalent bonds it contains
• Alloys are a mixture of metals with different-sized atoms that disrupt the lattice so layers cannot slide over each other as easily - stronger
• Allotropes of carbon:

  • Diamond - one of the hardest known substances due to very strong bonds
  • Graphite
  • Fullerenes/Nanotubes - used for electronics, composites, medical purposes
• Graphite:

  • Delocalised electrons form weak bonds between layers
  • Can conduct electricity as these bonds can move
  • Layers can slide over each other
  • Graphene = one layer
• Nanoparticles = 100-2500nm
• Coarse particles = >2500 e.g dust
• Fullerenes are useful due to high surface-to-volume ratio so fewer are needed for purpose. Double the length = half the ratio