Group 2

• These factors outweigh the effect of the increased nuclear charge and so it is easier to remove these electrons as we go down the group.
• Group II metals


  When they react, they lose the two electrons from their outer shell, so they act as reducing agents
• Group II metals


  • From magnesium to barium, they generally exhibit similar reactions
  • They are more reactive down the group because it is easier to lose the outer electrons
  • Beryllium has chemical and some physical properties which are more like those of aluminium than the other Group II elements, so its reactions are not considered here
• Reaction with oxygen


  1. Redox reaction

  2. Reactivity increases down the group

  3. 2Mg(s) + O2(g) → 2MgO(s)
• Oxides of Group II metals


  They are basic in character, reacting with water to form hydroxides
• Reaction with water


  1. Magnesium reacts very slowly with cold water but more vigorously with steam to form magnesium oxide and hydrogen

  2. Calcium reacts vigorously with cold water to form calcium hydroxide and hydrogen

  3. The other elements down the group react in a similar manner with increasing vigour

  4. The resulting solutions get more alkaline down the group as the solubility of the hydroxides produced increases
• Reaction with acids


  1. All members of the group react readily with acids to form hydrogen and the salt of the metal

  2. The reactivity increases down the group
• Uses of some compounds of Group II

  • Calcium oxide: making cement and mortar, drying agent
  • Calcium hydroxide: neutralising acidic soil, making bleaching powder, making limewater
  • Calcium carbonate: limestone blocks for building, removing SiO2 as slag in the blast furnace for the extraction of iron, making calcium oxide for cement
  • Magnesium oxide: for lining furnaces
• Group II elements from Mg to Ba


  • They are metals which react with water to produce hydrogen and a metal hydroxide
  • The atomic radii of the metals increases down the group
  • Group II metals burn in air to form oxides which are more soluble down the group
  • The reactivity of Group II elements with oxygen, water and dilute hydrochloric acid increases down the group
  • Many compounds of Group II metals have important uses
• Solubility of solid compounds


  Determined by the energy required to break the lattice into ions (reverse of lattice energy) and the energy released when ions are hydrated (hydration energy)
• Dissolving a group II sulphate has 3 main processes

  1. Reverse of lattice energy (-AH latt) MgSO4 (s) ->Mg2+ (g) + SO4 2+ (g)

  2. Enthalpy of hydration of the cation (AH hyd). Mg 2+(g) —> Mg 2+ (aq)

  3. Enthalpy of hydration of the anion (AH hyd). SO4 2- (g) -> SO4 2- (aq). AH sol = AH hyd- +. AH hyd+. - AH latt
• Lattice energy is inversely proportional to the sum of the radius of the cation and the radius of the anion
• If either ionic radius increases, lattice energy decreases
• The anion is constant
• Solubility of the sulphates in group II


  Decreases down the group. With math: if AH sol is endothermic it would be sparingly soluble, if exothermic it would be soluble
• Sulphate ions


  Detected by the relative insolubility of barium sulphate
• Test to detect sulphate ions


  1. Acidify the solution with nitric acid or hydrochloric acid

  2. Add aqueous barium chloride or aqueous barium nitrate
• Sulphate ions are present


  A white precipitate of barium sulphate is formed
• Group II carbonates and nitrates


  • More resistant to thermal decomposition down the group
  • Due to the decreasing degree of polarisation of the large CO3 or NO3 ion by the increasingly large metal cation
• Solubility of Group II sulphates


  • Decreases down the group
  • Can be explained in terms of the relative values of their enthalpy changes of hydration and lattice energies
• Testing for sulphate ions: barium chloride is added to a solution containing a sulphate, a white precipitate is formed
• As you go down group 2 the thermal decomposition of carbonates and nitrates increases. This is because of polarization where smaller cations ( atomic size) has more polarizing effect
• Polarization is the ability for a cation to attract and distort the spherical shape of an anion. The greater the polarization of the anion, the weaker the c-o bonds
• Solubility of carbonates

  Solubility of the carbonates decreases down the group. The decrease in solubility is similar to that of the sulphates. On going down the group, the decrease in lattice energy is small compared to the decrease in hydration energy. Thus the reverse lattice energy exceeds the hydration energy and the enthalpy of solution is positive.
• Solubility of the hydroxides

  The solubility of the hydroxides increases down the group. Since the hydroxide ion is not as large as the sulphate or carbonate ions, the lattice energy decreases significantly down the group. This outweighs the change in the hydration energy so the solubility of the hydroxides of group II elements increases down the group.
• Variation in solubility

  • Sulphates and carbonates: decrease in solubility down the group
  • Hydroxides: increase in solubility down the group