Properties of Substances

• What are the three states of matter?


  Solid, liquid, and gas
• At what point do melting and freezing occur?


  At the melting point
• At what point do boiling and condensing occur?


  At the boiling point
• How does particle theory explain changes in states of matter?


  • Energy needed to change state depends on forces between particles.
  • Nature of particles depends on bonding and structure.
  • Stronger forces lead to higher melting and boiling points.
• What are the limitations of the simple particle model?


  It assumes no forces, all particles are spheres, and spheres are solid.
• How are the states of matter represented in chemical equations?


  Solid (s), liquid (l), gas (g), and aqueous (aq)
• What are the properties of ionic compounds?


  • Regular structures (giant ionic lattices).
  • High melting and boiling points due to strong bonds.
  • Conduct electricity when melted or dissolved, not when solid.
• Why do ionic compounds conduct electricity when melted or dissolved?


  Because the ions are free to move and carry current.
• What states of matter are small molecules usually found in?


  Gases or liquids
• What are the properties of small molecules?


  • Usually have low boiling and melting points.
  • Weak intermolecular forces are broken during boiling or melting.
  • Larger molecules have higher melting and boiling points.
• Why don't small molecules conduct electricity?


  Because they do not have an overall electric charge.
• What are the characteristics of polymers?


  • Very large molecules.
  • Atoms linked by strong covalent bonds.
  • Strong intermolecular forces make them solids at room temperature.
• What are giant covalent structures and their properties?


  • Solids with very high melting points.
  • Atoms linked by strong covalent bonds.
  • Bonds must be overcome to melt or boil.
  • Examples: diamond, graphite, silicon dioxide.
• What are the properties of metals and alloys?


  • Metals have giant structures with strong metallic bonding.
  • Most metals have high melting and boiling points.
  • Alloys are harder than pure metals due to distorted layers.
• Why are metals good conductors of electricity?


  Because delocalised electrons carry electrical charge through the metal.
• Why are metals good conductors of thermal energy?


  Because energy is transferred by the delocalised electrons.