The Halogens
5 marks · EasyA laboratory investigation compares the ability of Group 7 elements to act as oxidising agents. The electronic structures of chlorine and bromine are shown below.
Explain, in terms of electron transfer, why the reaction between chlorine and iodide ions is classed as a redox reaction.
Chlorine is a stronger oxidising agent than bromine. Explain why, using ideas about the electronic configuration of halogen atoms.
State how the reactivity of the halogens changes as you go down the group.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) It is a redox reaction because iodide ions lose electrons (are oxidised) and chlorine gains electrons (is reduced). Electron transfer occurs between the two species. · must show iodide ions lose electrons, chlorine gains electrons/reduced
(b) Chlorine atoms have fewer electron shells than bromine atoms, so the outer electrons are closer to the nucleus and more strongly attracted. This means chlorine atoms gain electrons more easily and are stronger oxidising agents than bromine. · must show chlorine has fewer shells, outer electrons closer to nucleus, stronger attraction for electrons, chlorine gains electrons more easily
(c) The reactivity decreases as you go down the group. · must show reactivity decreases down the group
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Marking points
M1 (a) · 1 mark · Iodide ions lose electrons (oxidation) or reference to electron loss.
M2 (a) · 1 mark · Chlorine gains electrons (reduction) or clear statement of electron transfer; or chlorine is reduced.
E1 (b) · 1 mark · Chlorine has fewer shells/outer electrons closer to nucleus than bromine.
E2 (b) · 1 mark · Electrons are more strongly attracted/Chlorine gains electrons more easily.
A1 (c) · 1 mark · States reactivity decreases down the group.
Worked solution
a) In the reaction between chlorine and iodide ions:
Iodide ions, I^-, lose electrons to become iodine (oxidation). Chlorine, Cl2, gains those electrons to become Cl^- ions (reduction). It is a redox reaction as electron transfer occurs between the two.
b) Chlorine has a smaller atomic radius (fewer electron shells) than bromine. This means the electrons added are closer to the nucleus and feel a stronger attraction. Chlorine gains electrons more easily and is a stronger oxidising agent.
c) The reactivity of halogens decreases as you go down the group.