1. 1
   Three elements are identified only by their positions or electron configurations. Element J is in period 4 and group 15. Element L has the electron configuration 1s²2s²2p⁶3s²3p⁴. Element M is in period 4 and is the third element of the d-block.

   (a)

   What is the ground-state electron configuration of element J?

   [1 mark]

   • A[Ar]4s²4p³
   • B[Ar]3d³4s²
   • C[Ar]3d¹⁰4s²4p³
   • D[Ar]3d¹⁰4s²4p⁵

   (b)

   Which row correctly classifies elements J and L?

   [1 mark]

   • AJ: metal; L: non-metal
   • BJ: metalloid; L: non-metal
   • CJ: non-metal; L: metalloid
   • DJ: metalloid; L: metal

   (c)

   Deduce the condensed electron configuration of element M, explaining how its position in the periodic table is used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student shakes separate samples of sodium oxide (Na₂O), magnesium oxide (MgO), sulfur dioxide (SO₂) and sulfur trioxide (SO₃) with water containing universal indicator and records the colour of each mixture.

   (a)

   Which equation correctly represents the reaction of one of the oxides with water?

   [1 mark]

   • ASO₃(g) + H₂O(l) → H₂SO₃(aq)
   • BNa₂O(s) + H₂O(l) → Na₂O₂(s) + H₂(g)
   • CSO₂(g) + H₂O(l) → H₂SO₄(aq)
   • DNa₂O(s) + H₂O(l) → 2NaOH(aq)

   (b)

   What is the oxidation state of sulfur in the acid formed when sulfur dioxide reacts with water?

   [1 mark]

   • A+4
   • B+6
   • C+2
   • D−2

   (c)

   Predict the colour of universal indicator in the mixtures containing Na₂O and SO₃, and explain the change in acid–base character of the oxides across period 3 in terms of the elements' metallic character.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The atomic radii of the period 3 elements, in pm, are: Na 186, Mg 160, Al 143, Si 117, P 110, S 104, Cl 99. The ionic radii of some of their common ions, in pm, are: Na⁺ 102, Mg²⁺ 72, Al³⁺ 54, P³⁻ 212, S²⁻ 184, Cl⁻ 181.

   (a)

   Explain the trend in atomic radius from sodium to chlorine.

   [3 marks]

   (b)

   Using the data, explain why the Al³⁺ ion is much smaller than the P³⁻ ion, and why the ionic radius decreases from P³⁻ to Cl⁻.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a first experiment, small pieces of lithium, sodium and potassium are added separately to water containing a few drops of phenolphthalein indicator. Lithium floats and fizzes steadily; sodium melts into a ball and darts across the surface; potassium reacts violently and the gas produced ignites with a lilac flame. In each case the solution turns pink. In a second experiment, aqueous chlorine, bromine and iodine are each added to separate solutions of potassium chloride, potassium bromide and potassium iodide. Chlorine water turns potassium bromide solution yellow-orange and potassium iodide solution brown. Bromine water turns potassium iodide solution brown but causes no change with potassium chloride. Iodine solution causes no change with either potassium chloride or potassium bromide.

   (a)

   Describe and explain the trend in reactivity of the group 1 metals with water shown in the first experiment. Include a balanced equation for the reaction of potassium with water.

   [6 marks]

   (b)

   Deduce, with ionic equations, the reactions that occur in the second experiment, and explain the trend in reactivity of the group 17 elements that the results show.

   [6 marks]

   Total for question 4: 12 marks

End of questions