group 2

• Atomic radius


  The size of an atom
• Atomic radius increases down the group


  Atoms have more shells of electrons making the atom bigger
• 1st Ionisation Energy


  The energy required to remove the outermost electron from an isolated gaseous atom
• The outermost electrons are held more weakly


  They are successively further from the nucleus in additional shells
• The outer shell electrons become more shielded


  By the repulsive force of inner shell electrons
• Melting points decrease down the group


  The metallic bonding weakens as the atomic size increases
• The distance between the positive ions and delocalized electrons increases


  The electrostatic attractive forces between the positive ions and the delocalized electrons weaken
• Reaction of magnesium with oxygen

  1. Mg burns with a bright white flame

  2. MgO appears as a white powder

  3. 2 Mg + O2 → 2 MgO
• Reaction of magnesium with steam

  Mg(s) + H2O(g) → MgO(s) + H2(g)
• Reaction of group 2 metals with cold water

  1. Ca + 2 H2O (l) → Ca(OH)2 (aq) + H2 (g)

  2. Sr + 2 H2O (l) → Sr(OH)2 (aq) + H2 (g)

  3. Ba + 2 H2O (l) → Ba(OH)2 (aq) + H2 (g)
• The hydroxides produced make the water alkaline


  If they are soluble in water
• Reaction of magnesium with warm water

  Mg + 2 H2O → Mg(OH)2 + H2
• Titanium


  A very useful metal because it is abundant, has a low density and is corrosion resistant - it is used for making strong, light alloys for use in aircraft
• Extracting titanium


  1. TiO2 (solid) is converted to TiCl4 (liquid) at 900°C

  2. The TiCl4 is purified by fractional distillation in an argon atmosphere

  3. The Ti is extracted by Mg in an argon atmosphere at 500°C
• Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium
• Titanium cannot be extracted by electrolysis because it has to be very pure
• Titanium is extracted by reaction with a more reactive metal (e.g. Magnesium)
• Titanium is expensive because of the expensive cost of the magnesium, the batch process, the need for argon and to remove moisture, and the high temperatures required
• Flue gas desulfurisation


  1. Calcium oxide reacts with sulfur dioxide in the waste gases to form calcium sulfite

  2. SO2 + CaO → CaSO3
• Calcium sulfite can be used to make calcium sulfate for plasterboard
• Group II sulfates become less soluble down the group


  BaSO4 is the least soluble
• Testing for sulfate ions

  1. Acidified barium chloride solution is added

  2. A white precipitate of barium sulfate forms if sulfate ions are present
• BaSO4 is used in medicine as a 'Barium meal' given to patients who need x-rays of their intestines
• Barium compounds are toxic, but barium sulfate's low solubility means it is not absorbed into the blood
• If barium metal is reacted with sulfuric acid

  It will only react slowly, as the insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to further attack
• The same effect happens to a lesser extent with metals going up the group as the solubility of the sulfates increases
• The same effect does not happen with other acids like hydrochloric or nitric as they form soluble group 2 salts
• Hydrochloric acid is needed to react with carbonate impurities that are often found in salts which would form a white barium carbonate precipitate and so give a false result
• Precipitation reaction


  1. Mixing appropriate solutions of ions so that a precipitate is formed

  2. The precipitate is usually filtered, washed and dried
• Ionic equation


  Shows only the ions that are reacting and leaves out spectator ions
• Soluble salts


  • All sodium, potassium and ammonium salts
  • All nitrates
  • Most chlorides, bromides, iodides
  • Most sulfates
  • Sodium, potassium and ammonium carbonates
  • Sodium, potassium and ammonium hydroxides
• Insoluble salts


  • Silver, lead chlorides, bromides iodides
  • Lead, strontium and barium sulfates
  • Most other carbonates
  • Most other hydroxides
• Spectator ions


  Ions that are not changing state and not changing oxidation number
• Filtration


  The process of separating a solid from a liquid by passing the mixture through a filter
• Gravitational filtration


  1. Using a filter funnel and filter paper

  2. Used for small amounts of solid
• Vacuum filtration


  1. Using a Buchner flask and funnel connected to a water pump

  2. Used for larger amounts of solid