group 2

• Atomic radius


  Increases down the Group
• Atoms in Group 2


  • Have more shells of electrons making the atom bigger as you go down the group
• Electronic Structure


  Group 2 metals all have the outer shell s2 electron configuration
• First ionisation energy


  The energy needed to remove an electron from each atom in one mole of gaseous atoms
• First and second ionisation energies decrease down the group
• Reason for decreasing ionisation energies

  • The outermost electrons are held more weakly because they are successively further from the nucleus in additional shells
  • The outer shell electrons become more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons
• Reactivity of group 2 metals

  • Increases down the group
• Reason for increasing reactivity

  • As the atomic radii increase there is more shielding
  • The nuclear attraction decreases and it is easier to remove outer electrons
  • Cations form more easily
• Second ionisation energy


  The enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
• When the group 2 metals react, they lose their outer shell s2 electrons in redox reactions to form 2+ ions
• Mg will also react slowly with oxygen without a flame
• Mg ribbon will often have a thin layer of magnesium oxide on it formed by reaction with oxygen
• Cleaning Mg ribbon before reactions with acid

  Remove the magnesium oxide layer using emery paper
• Mg reacts with HCl

  Mg + 2HCl MgCl2 + H2
• MgO reacts with HCl

  MgO + 2HCl MgCl2 + H2O
• Reactions of group 2 metals with oxygen


  1. The group 2 metals will burn in oxygen

  2. Mg burns with a bright white flame

  3. 2Mg + O2 2MgO
• MgO


  A white solid with a high melting point due to its ionic bonding
• Melting points of group 2 metals

  • 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
• Reactions of group 2 metals with water

  1. Mg reacts in steam to produce MgO and H2

  2. The other group 2 metals will react with cold water with increasing vigour down the group to form hydroxides

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

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

  5. Ba + 2 H2O (l) Ba(OH)2 (aq) + H2 (g)
• Observations of group 2 metal reactions with water

  • Fizzing (more vigorous down group)
  • The metal dissolving (faster down group)
  • The solution heating up (more down group)
  • With calcium a white precipitate appearing (less precipitate forms down group)
• Mg will also react with warm water, giving a different magnesium hydroxide product
• Reactions of group 2 metals with acids

  1. The group 2 metals will react with acids with increasing vigour down the group to form a salt and hydrogen

  2. Ca + 2HCl (aq) CaCl2 (aq) + H2 (g)

  3. Sr + 2 HNO3 (aq) Sr(NO3)2 (aq) + H2 (g)

  4. Mg + H2SO4 (aq) MgSO4 (aq) + H2 (g)
• 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 will happen to a lesser extent with metals going up the group as the solubility increases
• The same effect does not happen with other acids like hydrochloric or nitric as they form soluble group 2 salts
• Calcium hydroxide


  • Reasonably soluble in water
  • Used in agriculture to neutralise acidic soils
  • If too much is added, excess will result in soils becoming too alkaline to sustain crop growth
• Magnesium hydroxide


  • Classed as partially soluble in water
  • A suspension of magnesium hydroxide in water will appear slightly alkaline (pH 9) so some hydroxide ions must therefore have been produced by a very slight dissolving
  • Used in medicine (in suspension as milk of magnesia) to neutralise excess acid in the stomach and to treat constipation
  • Mg(OH)2 + 2HCl MgCl2 + 2H2O
  • It is safe to use as it so weakly alkaline
• Action of water on oxides of elements in Group 2

  1. The group 2 oxides react with water to form hydroxides of varying solubility

  2. CaO (s) + H2O (l) Ca(OH)2 (aq)

  3. An aqueous solution of calcium hydroxide is called lime water and can be used a test for carbon dioxide. The limewater turns cloudy as white calcium carbonate is produced.

  4. Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O(l)
• Group 2 oxides are basic as the oxide ions accept H+ ions to become hydroxide ions in these reactions