February/March 2026 Paper 22

The Group 2 elements Mg to Ba show trends in their physical properties down the group.

Give the full electronic configuration of a calcium atom.

Explain the trend shown in the sum of the first and second ionisation energies, as proton number increases.

Write an equation to represent the third ionisation energy of barium.

Explain why the third ionisation energy of magnesium is much greater than the sum of its first and second ionisation energies.

When strontium reacts with water, an alkaline solution is produced.

Write an equation for this reaction. Include state symbols.

Samples of the alkaline solution produced in 1(b)(i) are tested with dilute HCl(aq) and separately with dilute H${}_2$SO${}_4$(aq). State what you would observe in each test.

The nitrates and carbonates of Group 2 elements decompose on heating.

State the trend in the thermal stability of the Group 2 carbonates down the group.

Write an equation for the thermal decomposition of Ca(NO${}_3$)${}_2$.

Calcium chlorate(I), Ca(ClO)${}_2$, is used for water purification in the same way as sodium chlorate(I), NaClO. Ca(ClO)${}_2$ can be prepared by the reaction of aqueous Ca(OH)${}_2$ with Cl${}_2$.

Write an ionic equation for the reaction of cold dilute OH${}^{-}$ ions with Cl${}_2$.

State why NaClO and Ca(ClO)${}_2$ are used in water purification.