3.2.2 Group 2, the alkaline earth metals

• The reactivity of group 2 is measured by their tendency to lose their 2 outer electrons.
• Group 2 metals react with oxygen by burning to produce a metal oxide. 
• Magnesium + steam = magnesium oxide and hydrogen.

  
  

  Mg + H20 (g) --> MgO + H2 
• Magnesium and warm water reaction:

  
  

  Mg + 2H20 --> Mg(OH)2 + H2 
• What is the observation for calcium when it reacts with cold water? Why?

  • It produces a white precipitate
  • as the product (Ca(OH)2) is sparingly soluble. 
• What is produced when group 2 metals react with cold water vs steam?

  • Cold Water - Metal Hydroxide
  • Steam - Metal Oxide
• Titanium is useful because it is:

  1. low density
  2. corrosion resistant
  3. abundant 
• Titanium is used for making strong light alloys in aircrafts
• Titanium can't be extracted with carbon because it would form titanium carbide - which is brittle. 
• Solubility of the Group 2 Metal Hydroxides:

  • Mg(OH)2 - sparingly soluble
  • Ca(OH)2 - slightly soluble
  • Sr(OH)2 - soluble
  • Ba(OH)2 - soluble 
• Solubility of sulfates:

  • MgSO4 - soluble
  • CaSO4 - slightly soluble
  • SrSO4 - insoluble
  • BaSO4 - insoluble
• Calcium Hydroxide is used in agriculture to neutralise acidic soils as it has a pH of 11 and is sparingly soluble.
• What is the trend in hydroxide solubility down group 2?

  • Increases down the group Mg(OH)₂ is almost insoluble Ba(OH)₂ creates a strong alkaline solution
• What is a use of BaSO4 ? Why is it safe? In barium meals to outline gut in X-rays Ba²+ is toxic but is fine as barium sulphate is insoluble
• Soluble salts:

  • All sodium, potassium, and ammonium salts.
  • All nitrates.
  • Most chlorides bromides and iodides.
  • Most sulfates. 
• Reactivity increases down the group 2 because:

  1. more shells therefore more shielding
  2. Atomic radius increases --> makes it easier to remove an electron as the attractive force of the nucleus is weaker 
• Melting points decrease down group 2. because metallic bonding weakens as atomic size increases.
• Insoluble Salts: Most carbonates, hydroxides, Silver, Lead, strontium, and barium sulfates 
• Write an equation for the first ionisation energy of magnesium Mg (g) → Mg+ (g) + e
• First ionisation energy decreases down the group 2 metals because:

  
  

  1. number of filled electron shells increases down the group
  2. → increased shielding, increased atomic radius
  3. → weaker force between outer electron and nucleus
  4. → less energy needed to remove electron
• Write an equation for the reaction of Barium and water Ba (s) + 2H2O (l) → Ba(OH)₂ (aq) + H₂ (g)
• Write an equation for the reaction of Magnesium and steam:

  Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
• What is the trend in sulphate solubility down group 2?

  • Decreases down group
  • MgSO₄ is soluble
  • BaSO₄ is insoluble
• Atomic radius increases down group 2 as there are more occupied electron shells down the group
• What are flue gases? Gases produced by power stations which are harmful to the environment
• What is Ca(OH)2 used for? Used to neutralise soil
• What is Mg(OH)2 used for? treating indigestion
• How can BaCl2 be used to test for sulfate ions?

  • Add to sample with HCl, white precipitate will form
  • if sulfate ions present Ba2+ + SO4 2- -> BaSO
• Write the equations for the extraction of Titanium using Magnesium:

  TiO2 + 2Cl2 + C → TiCl2 + CO2 TiCl2 (l) + 2Mg (s) → 2MgCl2 (s) + Ti (s)