Group 2

What are Group 2 elements called?

The alkaline earth metals

• They are silvery coloured and shiny although the heavier metals tarnish in air.

Trends of Group 2 elements down the group

• Melting points decrease.

• This is because positive ions become larger but have the same charge so there is a lower charge density so there are weaker forces of attraction between positive ions and delocalised electrons so the metallic bonding is therefore weaker.

• The melting point for Mg is much lower due to how the atoms arrange themselves in the lattice.

• Ionisation energy decreases due to more energy levels and increased shielding.

Uses of Group 2

• Magnesium is used in the process of extracting titanium.

• TiO2 → TiCl4 with carbon and Cl gas.

• TiCl4 (l) + 2Mg (s) → Ti (s) + 2MgCl2 (s)

• Calcium oxide and carbonate are used in flue gas desulphurisation forming calcium sulfite

• CaO (s) + SO2 (g) → CaSO3 (s)

• CaCO3 (s) + SO2 (g) → CaSO3 (s) + CO2 (g)

Reaction of Group 2 with water

• React to form metal hydroxide and hydrogen gas- redox reaction.

• Except Beryllium which is too unreactive.

Observation of Magnesium reacting with water and steam

• With water it reacts very slowly (unobservable) to form a white solid.

  Mg(OH)2 produced

• With steam there’s a bright white flame, white solid.

  MgO produced

Observation of Calcium with water

• Fizzing and white precipitate

Observation of Strontium with water

• Faster fizzing and white precipitate

Observation of Barium with water

• Vigorous fizzing and white precipitate

Solubility of hydroxide

• Magnesium hydroxide is insoluble

• Calcium is sparingly soluble

• Strontium is sparingly soluble

• Barium is soluble

Solubility of hydroxides (single charge anion) increases down the group whereas solubility of sulphates (double charge anion) decreases down the group.

Uses of magnesium hydroxide

• Forms a suspension in water called milk of magnesium.

• This acts as an antacid by neutralising excess stomach acid.

Uses of calcium hydroxide

• Used in agriculture where it is added to soil to raise the pH of acidic soils.

What is barium sulphate used for?

• Help take X-ray images as it’s radioactive.

• To test for sulphates as it’s insoluble.

• Add a few drops of HCl to remove false positives/ carbonates.

• Add a few drops of barium chloride and if a white precipitate forms, then that is barium sulphate.

  Ba 2+ (aq) + SO4 2- (aq) → BaSO4 (s)