Explaining the trend in the reactivity of the halogens
4 marks · NormalThis question is about how halogens react by gaining electrons.
Describe what happens to a bromine atom when it reacts to form a bromide ion.
Explain, using electron arrangement, why it is easier for chlorine to form an ion than bromine.
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(a) It gains one electron to form Br⁻ · must show Gains electron
(b) Chlorine has a smaller atomic radius than bromine, so when it gains an electron, the added electron is closer to the nucleus and more strongly attracted. It is therefore easier for chlorine to become an ion than bromine. · must show Chlorine smaller atom, New electron closer to nucleus, Stronger attraction, Easier to form negative ion
Common mistakes: Saying bromine loses electrons; Saying bromine is more reactive
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Marking points
B1 (a) · 1 mark · Says bromine atom gains one electron (to form Br⁻)
M1 (b) · 1 mark · Chlorine atom is smaller than bromine atom
M2 (b) · 1 mark · Electron added is closer to the nucleus in chlorine
A1 (b) · 1 mark · Stronger attraction makes it easier to form Cl⁻ than Br⁻
Worked solution
a) The bromine atom gains one electron to become a Br⁻ ion. b) Chlorine atoms are smaller than bromine atoms, so when chlorine gains an electron, the new electron is added closer to the nucleus and feels a stronger attraction, making it easier to form a Cl⁻ ion.