Group 2, the alkaline earth metals
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
The topic on one screen
- Group 2 metals react with water to give the hydroxide + hydrogen: M + 2H2O → M(OH)2 + H2. Reactivity increases down the group.
- Reactivity rises down the group because the outer electrons are further from the nucleus and more shielded, so they are lost more easily.
- Atomic radius increases down the group because each element has an extra occupied electron shell (not just 'more shielding').
- Hydroxide solubility INCREASES down the group; sulfate solubility DECREASES down the group (BaSO4 is essentially insoluble).
- Barium sulfate's insolubility makes it safe as a 'barium meal' — the toxic Ba2+ ions are not released.
- Uses: Mg to extract Ti; Ca(OH)2 to neutralise acidic soils; Mg(OH)2 and CaCO3 as antacids.
Where students actually lose marks
Explaining the increase in atomic radius down the group, 'more shielding' or 'more orbitals' alone were marked insufficient — you must say there is an extra electron shell.
June 2024 Paper 1 examiner report (Q09.1)
When barium reacts with dilute sulfuric acid the reaction slows quickly; very few said why — insoluble barium sulfate forms a layer on the metal and blocks further reaction.
June 2024 Paper 1 examiner report (Q09.3)
In reaction equations, watch the product: magnesium with water/steam trips students up, and the wrong formula (e.g. for magnesium phosphate) loses the balancing mark.
June 2023 Paper 1 examiner report (Q03.5)
Try it — exam-style
Write the equation for the reaction of strontium with water, and state the trend in reactivity of Group 2 metals with water down the group.
Explain why atomic radius increases down Group 2.
State the trend in solubility down Group 2 for (a) the hydroxides and (b) the sulfates.
Barium compounds are toxic, yet a suspension of barium sulfate is swallowed as a 'barium meal' before an X-ray. Explain why this is safe.
When barium is added to dilute sulfuric acid the reaction quickly slows down. Explain why.
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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Stuck on group 2, the alkaline earth metals?
Group 2 marks are won on precise trend explanations — 'extra shell', not 'more shielding' — and that's exactly what I drill. Your first lesson is free.