States of Matter

• Ideal gas


  • Molecules are in constant random motion in straight lines
  • Molecules are rigid spheres
  • Pressure is due to molecules colliding with the walls of the container
  • All collisions are elastic
  • Temperature is proportional to the average kinetic energy of the molecules
• Ideal gas behaviour


  • Temperature must be high enough above the boiling point so that there are no intermolecular forces between molecules
  • Pressure must be low enough so that the volume of the individual molecules is negligible relative to the volume of the container
• Limitations of ideal gas law

  • At high pressures the gas molecules get more crowded which isn't accounted for
  • At very low temperatures the effect of intermolecular forces is much more prominent as the molecules have less kinetic energy to overcome the attractions
• Ideal gas equation


  pV = nRT
• Converting units


  1. Pressure: 1 kPa = 1000 Pa, 1 atm = 101325 Pa, 1 bar = 100 kPa

  2. Volume: 1 m3 = 1000 dm3 = 1000000 cm3

  3. Temperature: 0 K = -273 °C
• Molar mass


  Can be determined using the ideal gas equation and the equation n = m/M where m is mass in g and M is the molar mass
• Liquids


  • Randomly arranged particles which are close together with some gaps
  • Particles have enough energy to prevent the intermolecular forces holding them in a fixed arrangement
  • Most liquids have a slightly lower density than the solid
• Melting


  1. Heat energy causes the particles in a solid to vibrate

  2. Eventually, the particles have enough energy to disrupt the regular arrangement and become a liquid
• Vaporisation


  Heat energy causes the particles in a liquid to move fast enough to break all the forces of attraction between them and become a gas
• Vapour pressure


  When a liquid evaporates in a closed container, the gaseous particles move around above the liquid and exert a pressure when they collide with the walls
• Types of crystalline solid lattice structures

  • Giant ionic lattice
  • Simple molecular (covalent) lattice
  • Giant molecular (covalent) structure
  • Hydrogen-bonded lattice
  • Metallic
• A finite resource is used up faster than it is replaced so it will run out if it is continually used
• Examples of finite resources are crude oil, copper and aluminium
• Recycling is important to reduce the rate at which resources are used up
• Effects of hydrogen bonding

  • Boiling and melting point are increased
  • Viscosity increases
  • Surface tension increases
• Predicting structure and bonding from data

  1. A high boiling point indicates a giant structure

  2. Compounds soluble in water tend to be ionic

  3. If the solid compound conducts electricity, it is likely to be a metal, graphite or graphene

  4. The appearance of a substance can be used to distinguish between giant structures