Summary AQA A-Level Chemistry 2.3 Group 7 (17) The Halogens
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Unit 3.2.3 - Group 7, the halogens
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AQA
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AQA Chemistry A Level Student Book
These are detailed Revision Notes for Topic 2.3 of AQA A-Level Chemistry (Group 7 (17), the Halogens). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- The halogens
- The chemical reactio...
AQA A-Level Chemistry 1.7 Oxidation, Reduction and Redox Reactions
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Unit 3.2.3 - Group 7, the halogens
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Group 7, the Halogens
10.1 The Halogens 10.1 The Halogens
- Halogens means salt forming. They react with. Many
10.2 the chemical reactions of the halogens
substances to form salts.
- As elements they are all diatonic. 10.3 reactions of halide ions
- At room temperature Fluorine is a pale-yellow gas, chlorine is 10.4 uses of chlorine
a green gas, bromine is a red-brown liquid and iodine is a black
solid. They get darker and denser down the group.
- Fluorine has some anomalous properties; its bonds are weaker than you would expect because it is such
a small atom that the pairs on one atom in F2 will repel those in the other.
- The atoms get bigger down the group because each element has an extra filled main level of electrons.
- Electronegativity decreases down the group because down the group each atom is larger, this means
attraction of the nucleus for the bonded electrons is weaker, offsetting the increase in nuclear charge
down the group.
- Down the group melting and boiling points increase, down the group each atom has more electrons, this
means the van der Waals forces are stronger and take more energy to overcome.
10.2 The Chemical Reactions of the Halogens
- Halogens usually react by gaining electrons to become negative ions with a charge of 1-.
- These are redox reactions – halogens are oxidising agents and are themselves reduced.
o E.g., Cl2 + 2e- à 2Cl-
- The oxidising ability of the halogens increases going up the group. Fluorine is one of the most powerful
oxidising agents known. They are less effective down the group because the atoms get larger, there is
more shielding so the attraction for the electrons to be gained is less. F- Cl- Br- I-
- Halogens will react with metal halides where the halide in the compound will be F2 / Yes Yes Yes
displaced by a more reactive halogen, this is a displacement reaction. Cl2 No / Yes Yes
o E.g., Cl2 + 2Br- à 2Cl- + Br2 Br2 No No / Yes
I2 No No No /
10.3 Reactions of Halide Ions
- Halide ions can act as reducing agents. They lose electrons and become halogen molecules. The larger the
ion, the easier it is to lose an electron so the reducing power increases down the group.
- Solid sodium halides react with concentrated sulfuric acid.
- Sodium Chloride and sulfuric acid:
o Gives off steamy fumes of hydrogen chloride and the solid product is sodium hydrogensulfate.
o NaCl(s) + H2SO4(l) àNaHSO4(s) + HCl(g). This is not a redox reaction, there are no change in
oxidation states because chloride ion is too weak a reducing agent; it is an acid-base reaction.
o This reaction can be used to prepare hydrogen chloride gas
- Sodium Bromide and sulfuric acid:
o Gives off steamy fumes of hydrogen bromide and brown fumes of bromine, colourless sulfur
dioxide is also formed.
o Two reactions occur, first hydrogensulfate and hydrogen bromide are produced in an acid-base
reaction, not redox as there are no changes in oxidation states.
o NaBr(s) + H2SO4(l) à NaHSO4(s) + HBr(g).
o However, bromide ions are strong enough reducing agents to reduce the sulfuric acid to sulfur
dioxide
o 2H+ + 2Br- + H2SO4(l) àSO2(g) + 2H2O(l) + Br2(l) this is a redox reaction the reaction are
exothermic and some of the bromine vaporises.
- Sodium Iodide and sulfuric acid:
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