IGCSE CHEMISTRY

• States of matter

  The different forms in which matter can exist
• States of matter


  • Solid
  • Liquid
  • Gas
• Solids


  • Have a definite shape
  • High density
  • Fixed volume
  • Non-fluid in nature
  • Closely-packed particles with barely any inter-molecular spaces
  • Particles are immobile but can vibrate about their fixed positions
  • Particles are arranged regularly in a lattice
• Liquids


  • Take the shape of their container
  • Moderate to high density
  • Fixed volume
  • Fluid in nature
  • Closely-packed particles with barely any inter-molecular spaces
  • Particles are able to move past one another
  • Particles are arranged irregularly
• Gases


  • Take the shape of their container
  • Low density
  • Don't have a fixed volume - expand to fill the container
  • Fluid in nature
  • Presence of large, inter-molecular spaces
  • Particles are mobile and move randomly
  • Particles are arranged irregularly
• Boiling


  Happens at a set temperature called the boiling point
• Evaporation


  Occurs at any temperature below the boiling point and above the freezing point (liquid)
• Condensation


  The process in which a gas converts into a liquid. It happens at the same temperature as the boiling point
• As temperature decreases, the energy of particles will decrease, making it move more slowly</b>
• Condensation and Freezing are both energy given out reactions
• Melting


  The process in which a solid converts to a liquid. It happens at a set temperature called the melting point
• Freezing


  The process in which a liquid converts to a solid. It happens at the same temperature as the melting point
• Cooling curve


  1. Particles of gas move slower and slower, gas contracts

  2. Particles get closer, inter-molecular bonds start to form at condensation point

  3. Temperature stops falling, energy released by bond formation cancels energy lost due to cooling

  4. Once all gas turned to liquid, temperature starts falling again, liquid contracts until freezing point

  5. At freezing point, inter-molecular bonds between liquid molecules start to develop to form solid

  6. At freezing point, temperature remains constant until all liquid has solidified
• Heating curve


  1. Solid particles vibrate faster, solid expands

  2. At melting point, inter-molecular bonds between particles begin to break down

  3. Temperature remains constant until all solid has turned to liquid, as energy received cancels energy used to break bonds

  4. Once all solid has turned to liquid, temperature starts rising again, liquid expands until boiling point

  5. At boiling point, inter-molecular bonds between liquid molecules start to break down to form gas

  6. At boiling point, temperature remains constant until all liquid has vaporized
• Gases


  Compressible in nature, volume can be influenced by changing pressure
• Increase in external pressure


  Contraction (decrease) in gas volume
• Decrease in external pressure


  Expansion (increase) in gas volume
• Increase in temperature


  Increased kinetic energy of gas molecules, increased internal pressure and volume
• Decrease in temperature


  Decreased kinetic energy of gas molecules, decreased internal pressure and volume
• Temperature and volume of gases are directly proportional
• External pressure and volume of gases are inversely proportional
• Diffusion


  The net movement of particles from a region of higher concentration to a region of lower concentration, as a result of their random movement until equilibrium is reached
• The rate of diffusion is most rapid in gases > liquids > solids
• Relative molecular mass and diffusion rate

  At the same temperature, molecules with lower mass move faster on average than those with higher mass
• HCl and NH3 diffusion experiment

  Ammonia with lower molecular mass diffused faster than hydrochloric acid with higher molecular mass
• Atom


  The smallest particle of matter made of protons, neutrons and electrons
• Types of substances


  • Elements
  • Compounds
  • Mixtures
• Elements


  Group of atoms that share the same number of protons, cannot be broken down into simpler substances by chemical methods
• Compounds


  Two or more elements chemically bonded together
• Mixtures


  Two or more elements not chemically bonded together
• Atom structure


  • Mostly space with a positively charged nucleus consisting of protons and neutrons, and electrons in the empty space around the nucleus
  • Electrons and protons have opposing and equal charges, so the atom's overall charge is neutral
  • Neutrons hold the nucleus together

  
• Proton number (atomic number)

  The number of protons in the nucleus of an atom, unique to each element
• Nucleon number (mass number)

  The total number of protons and neutrons in the nucleus of an atom
• For a neutral atom, the number of protons and electrons are equal
• Electron shells


  • The energy levels of the shells increase as their distance from the nucleus increases
  • The first shell has a maximum capacity of 2 electrons, while each subsequent shell can hold up to 8 electrons
• The general full electronic configuration is (2.8.8)
• Group VIII noble gases have a full outer shell
• The number of outer shell electrons is equal to the group number in Groups I to VII

  
• The number of occupied electron shells is equal to the period number
• Calculating relative atomic masses

  Most elements exist naturally as a mixture of isotopes, using the data on the abundance of these naturally occurring isotopes, we can calculate the mass relative atomic mass of the element