chemistry

• Metallic bonds are formed between metal atoms where electrons are delocalized and free to move throughout the structure.
• Covalent bonding occurs when two non-metal atoms share one or more pairs of electrons.
• The boiling point of an ionic compound increases with increasing size of the ions because larger ions require more energy to overcome their stronger attraction.
• Ionic compounds have high melting points due to strong electrostatic forces holding the positive and negative ions together, while covalent compounds have low melting points as there is no charge separation and weak intermolecular forces hold them together.
• Covalent bonds occur when atoms share electrons to achieve a full outer shell and become more stable.
• Ionic bonds form between atoms when one atom transfers electrons to another, resulting in positively and negatively charged ions.
• Atoms can gain or lose electrons to form ions.
• The pH scale ranges from 0-14 with 7 being neutral.
• The number of protons is equal to the atomic number.
• Solid


  Fixed shape, do not flow, high density, particles arranged regularly and packed closely together, vibrate in fixed positions, strong forces between particles, small amount of kinetic energy
• Liquid


  Flow easily, fixed volume but will flow to fit shape of container, particles are mostly touching with some gaps, particles move about at random, medium forces between particles, moderate amount of kinetic energy
• Gas


  No fixed volume or shape, less dense than same volume of solid or liquid, particles move at random and quickly, particles are far apart, weak forces between particles, high amount of kinetic energy, collide with each other and sides of container
• Solid → liquid


  Melting
• Liquid → gas


  Boiling / Evaporating
• Gas → liquid


  Condensing
• Liquid → solid


  Freezing
• When water vapour cools to form liquid water

  Particles lose kinetic energy, particles move closer together, particles move slower and less randomly
• When liquid water boils to form water vapour


  Particles gain kinetic energy
• Solids


  • Have a fixed shape
  • Do not flow
  • High density
  • Particles arranged regularly and packed closely together
  • Vibrate in fixed positions
  • Strong forces between particles
  • Small amount of kinetic energy
• Liquids


  • Flow easily
  • Fixed volume but will flow to fit shape of container
  • Particles are mostly touching with some gaps
  • Particles move about at random
  • Medium forces between particles
  • Moderate amount of kinetic energy
• Gases


  • No fixed volume or shape
  • Less dense than same volume of solid or liquid
  • Particles move at random and quickly
  • Particles are far apart
  • Weak forces between particles
  • High amount of kinetic energy
  • Collide with each other and sides of container
• What happens when liquid water boils to form water vapour


  1. Particles gain kinetic energy

  2. Particles move further apart

  3. Particles move quicker and more randomly
• What happens when liquid water cools to form ice


  1. Particles lose kinetic energy

  2. Particles move closer together

  3. Particles move slower and less randomly
• What happens when ice melts to form liquid water


  1. Particles gain kinetic energy and vibrate more

  2. Particles move further apart as forces of attraction are overcome

  3. Particles move quicker and more randomly
• How does evaporation occur


  1. Particles in liquid have differing amounts of energy

  2. Particles with the greatest amount of kinetic energy break away from surface of liquid

  3. Average kinetic energy of remaining particles is lowered

  4. In a closed container both evaporation and condensation occur simultaneously
• What happens to the volume of a gas when its temperature increases

  Volume of gas increases
• Use kinetic theory to explain why the volume of a gas increases when temperature increases


  1. Particles gain kinetic energy

  2. Particles move quicker and more randomly

  3. Particles move further apart
• What happens to the pressure of a gas in a container when its temperature increases

  Pressure increases
• Use kinetic theory to explain why pressure in a container increases when temperature increases


  1. Particles have more kinetic energy → move faster

  2. Each particle collides with greater force → increases pressure

  3. Collide more frequently with container walls → increases pressure
• What happens to the pressure of a gas in a container when the volume decreases

  Pressure increases
• Use kinetic theory to explain why pressure in a container increases when volume decreases


  1. Temperature remains constant → average kinetic energy of gas particles stays the same

  2. However container is smaller → particles collide with walls more often

  3. Increased frequency of collisions → increase in pressure
• Diffusion


  • Net movement of particles
  • From an area of high concentration to low concentration
• Factors affecting rate of diffusion


  • Molecular mass (Mr) - the lower the mass, the faster a gas diffuses
  • Temperature - the greater the temperature, the greater the kinetic energy of the particles, rate of diffusion increases
• How can diffusion be demonstrated experimentally


  • Use cotton wool balls soaked in ammonia (NH3) and hydrochloric acid (HCl)
  • Place cotton wool at either end of a sealed tube
  • White ring of ammonium chloride forms closer to HCl end
  • Tells you that NH3 diffuses faster
  • NH3 has a lower Mr, so has lower mass, diffuses more quickly than HCl
• Element


  • A substance which contains one TYPE of atom only
  • Cannot be split into anything simpler by any chemical means
• Compound


  A substance made up of two or more elements chemically combined
• Mixture


  A substance made up of two or more elements NOT chemically bonded together
• Pure substance


  • Contains one type of material only
  • e.g. one type of element or molecule
• Melting and boiling points of pure substances


  • Fixed
  • e.g. boiling point of pure water is exactly 100°C
  • e.g. melting point of pure water is exactly 0°C
• Melting and boiling points of mixtures


  • Melt over a range of temperatures
  • Boil over a range of temperatures