AQA Chemistry Unit 2: 12 Group 2, the Alkaline Earth Metals

• Group 2: called alkaline earth metals due to their oxides and hydroxides being alkaline
• They are S-Block element but are less reactive than Group 1

Electron Arrangement

• All have 2 electrions in the highest energy level

The Sizes of the Atoms

• Atoms get bigger down the group
• Atomic radii increases due to extra filled energy level

Melting Points

• High melting points due to giant metallic structure.
• Decreases down the group due to sea of delocalised electrons being further away from the nucleus so metallic bonds strength decreases down the group
• Magnesium has the lowest melting point due to different lattice arrangement of atoms

Ionisation Energies

• All reactions in group 2 they lose their 2 highest energy electrons to form positive ions
• M -> M2+ + 2e- : 1st and 2nd Ionisation energies together
• Both the 1st and 2nd ionisation energies decrease down the group
• Takes less energy to remove the electrons as they become further away from the nucleus
• The nucleus also experiences more shielding by extra electron energy level

• Oxidation is the loss of electrons, all group 2 metals are oxidised
• The metals have oxidation states that change from 0 to 2+
• These are redox reactions

Reaction with Water

• The metals get more reactive down the group
• M(s) + 2H2O(l) -> M(OH)2(aq) + H2(g)
• Magnesium reacts slowly with cold water but rapidly with steam to form an alkaline oxide and hydrogen:
• Mg(s) + H20(g) -> MgO(s) + H2(g)
• Calcium reacts more vigorously, then strontium and barium
• Calcium Hydroxide (Slaked Lime) is used to treat acidic soil

Hydroxide

• Down the group the hydroxides become more soluble
• The hydroxides are white solids
• Magnesium Hydroxide is almost insoluble
• Calcium hydroxide is sparingly soluble, its used in lime water
• Strontium Hydroxide is more soluble
• Barium Hydroxide dissolves to produce a strong alkaline solution
• Ba(OH)2(s) + aq -> Ba2+(aq) + 2(OH)-(aq)

Sulfates

• They become less soluble down the group
• Barium Sulfate:outlines the gut as it absorbs x-rays and since it's insoluble it's safe
• Barium sulfate is used to test sulfate ions: first acidified with nitric/hydrochloric acid, barium chloride is added to the solution, if sulfate is present a white precipitate is formed
• Ba2+(aq) + SO4-2(aq) -> BaSO4(s)
• The acid removes carbonate ions