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Electron shielding and calcium reactivity
A calcium atom is larger than a magnesium atom.
Explain why calcium reacts more vigorously than magnesium with hydrochloric acid of the same concentration.
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Marking points
- 1 Links calcium’s larger atom to outer electrons being farther from the nucleus or to more occupied shells.
- 2 Explains weaker nuclear attraction or greater shielding of calcium’s outer electrons.
- 3 Concludes that calcium loses electrons/forms positive ions more easily.
Full-mark answer
Calcium has an extra occupied electron shell, so its outer electrons are farther from the nucleus and more shielded than magnesium’s. They are therefore less strongly attracted to the nucleus and are lost more easily, so calcium forms positive ions and reacts more vigorously.
Why this answer loses marks
Calcium reacts faster simply because its atom is bigger.
Size alone is not enough; connect distance and shielding to weaker attraction and easier electron loss.