group 2

• atomic radius increases down group 2 as atoms have more shells of electrons making the atom bigger
• melting points decrease down group 2

  metallic bonding weakens as atomic size decreases

  the distance between positive ions and delocalised electrons increases and the electrostatic forces of attraction between them weaken
• 1st IE decreases down group

  outermost electrons held more weakly because they are successively further from the nucleus in additional shells

  the outer shell electrons become more shielded from attraction of the nucleus by the repulsive force of inner shell electrons
• reactivity of group 2 metals increases down the group
• Mg burns in oxygen with a bright white flame

  2Mg + O2 --> 2MgO

  MgO is a white solid powder with a high melting point due to its ionic bonding
• Magnesium reacts slowly in oxygen without a flame

  magnesium ribbon will often have a thin layer of magnesium oxide on it formed by the reaction with oxygen in the air

  2Mg + O2 --> 2MgO
• magnesium oxide needs to be removed by emery paper before doing reactions with magnesium ribbon
• if testing for reaction rates with Mg and acid, an uncleaned Mg ribbon would give a false result because both the Mg and MgO would react at different rates

  Mg + 2HCl --> MgCl2 + H2

  MgO + 2HCl --> MgCl2 + H2O
• magnesium reacts in steam to produce magnesium oxide and hydrogen

  burns with a bright white flame and MgO appears as a white powder
• magnesium reaction with steam

  Mg (s) + H2O (g) --> MgO (s) + H2 (g)
• Mg reacts with warm water to produce magnesium hydroxide

  Mg + 2H2O --> Mg(OH)2 + H2
• magnesium reacts slower with water than steam

  it does not produce a flame with water
• other group 2 metals react with cold water more vigorously down the group to form hydroxides
• calcium and cold water

  Ca + 2H2O --> Ca(OH)2 + H2
• Strontium and cold water

  Sr + H2O --> Sr(OH)2 + H2
• barium reacting with cold water

  Ba + 2H2O --> Ba(OH)2 + H2
• reactions with cold water observations

  fizzing (more vigorous down group)

  metal dissolving (faster down group)

  solution heating up (more down group)
• when calcium reacts with cold water a white precipitate appears, less precipitate forms down the group with other metals
• titanium is abundant, has low density and is corrosion resistant

  it is used for making strong, light alloys in aircraft
• titanium is extraction by reaction with a more reactive metal like magnesium
• titanium cannot be extracted by carbon because titanium carbide (TiC) is formed rather than titanium
• titanium cannot be extracted by electrolysis because it has to be very pure
• steps in extracting titanium

  1. TiO2 (solid) is converted to TiCl4 (liquid) at 900℃
  2. TiCl4 is purified by fractional distillation in an argon atmosphere
  3. Ti is extracted by Mg in argon atmosphere at 500℃
• extracting titanium equations

  TiO2 + 2Cl2 + 2C --> TiCl4 + 2CO

  TiCl4 + 2Mg --> Ti + 2MgCl2
• titanium is expensive because magnesium used to extract is expensive
• titanium is expensive because the batch process involves filling up and emptying reactors which is slow

  requires more labour and the energy is lost when the reactor is cooled down after stopping
• titanium is expensive because of the argon atmosphere required and need to remove moisture as TiCl4 is susceptible to hydrolysis
• titanium is expensive because it requires high temperatures in all steps
• calcium oxide can be used to remove SO2 from the waste gases from furnace (coal fired power station) by flue gas desulfurization
• flue gas desulfurization

  gases pass through a scrubber containing basic calcium oxide which reacts with the acidic sulfur dioxide in a neutralisation reaction
• Flue gas desulfurization equation

  SO2 + CaO --> CaSO3 (calcium sulfite)
• calcium sulfite produced from flue gas desulfurization can be used to make calcium sulfate from plasterboard
• group 2 hydroxides become more soluble down the group
• all group II hydroxides when not soluble appear as white precipitates
• magnesium hydroxide is insoluble in water
• ionic equation for formation of Mg(OH)2 (s)

  Mg2+ (aq) + 2OH- (aq) --> Mg(OH)2 (s)
• a suspension of magnesium hydroxide in water will appear slightly alkaline so some hydroxide ions must have been produced by a very slight dissolving
• magnesium hydroxide is used in medicine (milk of magnesia) to neutralise excess stomach acid and treat constipation
• milk of magnesia

  Mg(OH)2 + 2HCl --> MgCl2 + 2H2O
• magnesium hydroxide is safe to use because it is so weakly alkaline and preferred over calcium carbonate as it will not produce carbon dioxide