1. 1
   A technician adds a small volume of chlorine water to separate test tubes, each containing a colourless aqueous solution of a different potassium halide: potassium bromide and potassium iodide.

   (a)

   A student adds chlorine water to a colourless solution of potassium bromide, and the solution turns orange. What does this show?

   [1 mark]

   • AChlorine has displaced bromine from potassium bromide
   • BBromine has displaced chlorine from potassium chloride
   • CNo reaction has taken place
   • DPotassium metal has been produced

   (b)

   Which halogen is more reactive, based on the technician's experiment?

   [1 mark]

   • AThey are all equally reactive
   • BBromine
   • CIodine
   • DChlorine

   (c)

   Explain why a more reactive halogen, such as chlorine, is able to displace a less reactive halogen, such as bromine, from an aqueous solution of its salt.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher compares the electronic structures of fluorine, chlorine and iodine on the board, highlighting the energy level (shell) that contains the outer electrons of each atom, to explain the trend in reactivity down Group 7.

   (a)

   Going down Group 7, what happens to the energy level (shell) occupied by the outer electrons of the halogen atoms?

   [1 mark]

   • AIt stays exactly the same
   • BIt gets closer to the nucleus (lower energy level)
   • CIt gets further from the nucleus (higher energy level)
   • DIt disappears completely

   (b)

   Based on this trend in outer electron energy level, how does the ease of gaining an electron change going down Group 7?

   [1 mark]

   • AIt becomes easier to gain an electron
   • BIt becomes harder to gain an electron
   • CIt has no effect on gaining electrons
   • DHalogens lose electrons instead going down the group

   (c)

   Use the idea of energy levels to explain why reactivity of the halogens decreases going down Group 7.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student studies the electronic structures of Group 1 metals (lithium, sodium, potassium) alongside those of Group 7 halogens (fluorine, chlorine, bromine), comparing how outer electron energy levels change going down each group.

   (a)

   A student compares the electronic structures of lithium, sodium and potassium, noting that each has just one electron in its outer energy level, but the energy levels are progressively further from the nucleus going down the group. Explain how this relates to the trend in reactivity of Group 1 metals.

   [3 marks]

   (b)

   Contrast the reactivity trends of Group 1 and Group 7 as the outer electron energy level increases going down each group, explaining why one group becomes more reactive while the other becomes less reactive.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A research scientist is asked to determine the relative reactivity of the halogens chlorine, bromine and iodine using displacement reactions with aqueous potassium halide solutions, and to explain the underlying cause of the reactivity trend.

   (a)

   Describe how a scientist could use halogen displacement reactions in aqueous solution to work out the order of reactivity of chlorine, bromine and iodine, including expected observations, and explain the results in terms of energy levels of outer electrons.

   [6 marks]

   (b)

   A separate investigation compares the reactivity of the Group 1 metals lithium, sodium and potassium by timing how long each takes to fully react with water. Explain, using the concept of outer electron energy levels, why potassium reacts fastest and lithium reacts slowest, and explain why this trend is the opposite of the trend seen in Group 7.

   [6 marks]

   Total for question 4: 12 marks

End of questions