Group 2: The Alkaline Earth Metals

Presenter: Chris Harris

Overview

• Revision video specific to the AQA syllabus.
• PowerPoint available for purchase via link in description.

Atomic Radius

• Group 2 elements form +2 ions when they react (configuration ends in S2).
  • e.g., Beryllium (Be), Magnesium (Mg), Calcium (Ca) end in S2.
• Atomic radius increases down the group due to adding extra electron shells.

Ionization Energy

• First ionization energy decreases as we go down the group.
  • Extra electron shells lead to increased shielding.
  • Weaker attraction between nucleus and outer electrons.
• Increased number of protons doesn't compensate for shielding effect.

Melting Points

• Generally decrease down the group.
  • Due to increased size of metal ions, but constant delocalized electrons and charge causing weaker metallic bonding.
  • Magnesium is an exception due to structural arrangement.

Reactions with Water

• Group 2 metals react with water forming metal hydroxides and hydrogen gas.
  • e.g., Strontium with water forms Sr(OH)2 and H2.
  • Reactivity increases down the group (no reaction with Barium).
  • Magnesium reacts slowly with cold water but more vigorously with steam, forming MgO and H2.

Solubility

• Group 2 hydroxides and sulfates have opposite solubilities as we go down the group.
  • Hydroxides become more soluble.
  • Sulfates become less soluble.

Test for Sulfates

• Use Barium Chloride to test for sulfates.
  • Add HCl to remove carbonates (prevent false positives).
  • Add Barium Chloride: A white precipitate indicates presence of sulfate (BaSO4).

Neutralization Uses

• Group 2 compounds are used to neutralize acids.
  • Calcium Hydroxide (Ca(OH)2) for acidic soils.
  • Magnesium Hydroxide (Mg(OH)2) for antacids.
  • Neutralization ionic equation: H+ + OH- = H2O.

Barium Meals

• Used to identify issues with the digestive tract via x-rays.
  • Patient drinks a suspension of Barium Sulfate (insoluble and non-toxic).
  • Barium absorbs x-rays, highlighting areas in digestive tract.

Extraction of Titanium

• Magnesium is used to extract Titanium from its ore (rutile).
  • Titanium dioxide (TiO2) converted to Titanium Chloride (TiCl4) via heating with carbon and chlorine.
  • TiCl4 purified and reduced by Magnesium at high temperatures.
  • Reaction: TiCl4 + 2Mg = Ti + 2MgCl2.

Removal of Sulfur Dioxide

• Calcium Carbonate (CaCO3) and oxide used to remove SO2 emissions.
  • Process called 'wet scrubbing'.
  • Produces calcium sulfate (CaSO4), useful for making plasterboards.

Conclusion

• End of the Group 2 revision overview.
• PowerPoint available for purchase via link in description.