3.2.2 Group 2: The Alkaline Earth Metals

• The Group 2 metals lose 2 electrons to form 2+ ions when they react in order to achieve a full outer shell.
• Group 2 elements are called alkali earth metals.
• The atomic radius of group 2 metals increases down the group due to increasing number of electrons shells.
• Reactivity increases down group 2.
• Reactivity increases down group 2 because increased electron shielding means valence electrons are easier to lose.
• The first ionisation energy decreases down group 2.
• The first ionisation energy decreases down group 2 because atomic radius increases as does shielding.
• The melting points of group 2 metals decreases down group 2 because they are metallic meaning larger ions within the metallic structure have weaker attractive forces as they have to act over a greater distance.
• The group 2 metals react with water in a redox reaction to form a metal hydroxide and hydrogen.
• The metal hydroxide forms as an alkaline solution.
• Magnesium reacts very slowly with liquid water, however is much faster with steam because it provided the reaction with extra energy. When steam is used, Mg burns with bright white flame to form H2 and MgO, a white powder.
• Solubility of group 2 metal hydroxides increases down the group.
• Magnesium hydroxide is the least soluble and barium hydroxide is the most soluble.
• Magnesium hydroxide is used in medicines such as antacid as it is alkaline and can neutralise acids. It is similarly used in agriculture to neutralise acidic soils.
• Solubility of group 2 sulphates decreases down the group.
• Magnesium sulphate is the most soluble and barium sulphate is the least.
• The insolubility of barium sulphate means it can be used in medicines such as barium meals. It is toxic if it enters the blood, however due to its insolubility it cannot be absorbed into the blood.
• Barium chloride is used as a test for sulphate ions as it reacts to form barium sulphate which forms as a white precipitate when sulphate ions are present.
• Magnesium is used in the extraction of titanium from titanium chloride via a displacement reaction.
• Calcium oxide reacts with sulphur dioxide to remove it from factory pollutants and prevent it being released into the atmosphere. This forms calcium sulphate and water.
• Down group 2 atomic radius increases due to the greater number of electrons meaning number of shells increases.
• Down group 2 reactivity increases because the atomic radius increases meaning there is less attraction between the nucleus and valence electron.
• Down group 2, first ionisation energy decreases due to increased electron shielding and increased atomic radius making it easier to remove the valence electron as nuclear attraction decreases.
• Down group 2, melting points generally decrease because the size of the metal ion increases meaning electrons are further away from the nucleus with less attraction so less energy is required to break the bonds.
• Magnesium is an exception to the trend of melting points due to it having a different crystal structure.
• Solubility of group 2 hydroxides increases down the group.
• Mg(OH)2 is the least soluble group 2 hydroxide.
• Solubility of group 2 Sulphates decreases down the group.
• The test for sulphate ions is carried out by adding acidified barium chloride to the sample and if a white precipitate is formed, sulphate ions are present.
• In the test for sulphate ions, ACIDIFIED barium chloride is added to remove any carbonate ions which will produce a white precipitate too.
• Magnesium is used as the reducing agent in the extraction of titanium from TiCl4.
• The equation for the extraction of titanium from TiCl4 is:

  TiCl4 (g) + 2 Mg (l) ---> Ti (s) + 2 MgCl2 (l)
• Magnesium hydroxide is used to neutralise stomach acid.
• Barium sulphate is used in barium meals which help to diagnose stomach, oesophagus and intestinal problems.
• Calcium Hydroxide is used to neutralise acidic soil in agriculture.
• Calcium Carbonate and Calcium Oxide are used to remove sulphur dioxide from flue gases.
• Sulphur dioxide is removed from flue gases when SO2 reacts with alkaline slurry to form CaSO3.