5.2,5.3,5.4 chem notes

• Intermolecular forces


  Forces of attraction between molecules
• Types of substances


  • Ionic compounds
  • Simple covalent molecules
  • Giant covalent molecules
  • Macromolecules
• Ionic compounds


  • Strong electrostatic attraction between the oppositely charged ions in the giant ionic lattice structure
  • Hard as the strong electrostatic attraction cause the oppositely charged ions to resist motion
  • Brittle as when enough force is applied, the ions move away from their lattice positions and ions of the same charge approach each other, the repulsive force becomes larger than the attractive forces and the lattice structure shatters
  • Soluble in water but insoluble in organic solvents
  • Cannot conduct electricity in solid state because the oppositely charged ions are electrostatically attracted in the lattice and can only vibrate about their fixed positions, but can conduct electricity in molten and aqueous state due to the presence of mobile ions that act as charge carriers
• Simple covalent molecules


  • Weak intermolecular forces of attraction between molecules in the simple molecular structure
  • Lower melting and boiling points, exist in liquid or gaseous state due to the small amount of energy needed to overcome the weak intermolecular forces
  • Soluble in water but insoluble in organic solvents
  • No mobile ions or electrons, hence cannot conduct electricity in any state
  • Exception: Hydrogen chloride & ammonia gas can dissolve in water to form ions
• Giant covalent molecules


  • Extensive, strong covalent bonds between the atoms in the giant three-dimensional molecular structure
  • Very high melting and boiling points, exist as solids due to the large amount of energy needed to break the strong covalent bonds
  • Very hard as a large amount of energy is needed to break the giant three-dimensional molecular structure
  • Insoluble in water and organic solvents
  • No mobile ions or electrons, hence cannot conduct electricity in any state
• Macromolecules


  • Many small covalent molecules joined together into a macromolecule (long chain molecule) through a reaction
  • Higher melting and boiling points as compared to simple covalent molecules
• Malleable


  Able to be bent/flattened without breaking
• Ductile


  Able to be pulled into a wire
• Metals


  • Strong electrostatic attraction between positively charged metal ions and the 'sea of delocalised electrons'
  • High melting and boiling points because of the large amount of energy needed to overcome the strong electrostatic attraction
  • Melt over a range of temperatures because the sea of delocalised electrons are more mobile in the giant metallic structure
  • Very hard as a large amount of energy is needed to break the giant three-dimensional metallic structure
  • Presence of sea of delocalised electrons as charge carriers, hence good electrical conductors
  • Good conductors of heat, the delocalised electrons allow efficient transfer of heat throughout the giant metallic lattice
• Alloys


  • Mixture of a metal with one or more other elements
  • Harder and stronger than pure metals because the addition of a different sized atom disrupts the regular lattice arrangement, requiring a larger force to make the layers slide over each other