A level Chemistry · Edexcel 9CH0 · Topic 4A
Group 2
Key points
- Group 2 metals react with water to form hydroxides and hydrogen (Mg reacts very slowly with cold water but burns in steam to give MgO); reactivity increases down the group as ionisation energies fall.
- They burn in oxygen to give oxides, MO; react with chlorine to give MCl₂.
- Oxides and hydroxides are basic: they neutralise acids and form alkaline solutions (pH rises down the group as solubility rises).
- Solubility: hydroxides become more soluble down the group; sulfates become less soluble (BaSO₄ is insoluble).
- Thermal stability of carbonates and nitrates increases down the group: larger cations with lower charge density polarise the anion less.
- Group 1 compounds are more stable than Group 2 ones. Nitrates give MO + NO₂ + O₂ (Group 2) and MNO₂ + O₂ for most Group 1.
- Flame colours: Li red, Na yellow, K lilac, Ca orange-red, Sr crimson, Ba apple-green. Heat excites electrons, which emit light as they fall back.
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Group 2 metals (magnesium to barium) are reactive metals that form 2+ ions. Their chemistry shows clear trends down the group that you can explain from ionisation energies, ion size and polarisation.
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