Detailed and comprehensive notes on group 7 (unit 3.2.3 of AQA AS level chemistry). Covers group 7 properties and trends, halogen displacement reactions, reactions with sulfuric acid, tests for group 7 ions and uses of chlorine.
Boiling Points Increase Down the Group
• Due to increasing strength of van der Waals forces as the size and relative mass of the molecules
increases.
• (Trend is displayed in the changes of physical state from fluorine (gas) to iodine (solid).)
Electronegativity Decreases Down the Group
• Increased shielding offsets increased nuclear charge, so the major variant is the distance between the
outermost electron and the nucleus.
• This distance increases, so the attraction between the outermost electron and the nucleus decreases.
Oxidising Power Decreases Down the Group
• Reactivity decreases down the group, as there is less attraction between the nucleus and outer electron.
• Hence the ability of the halogen to oxidise another atom or reduce itself decreases.
• Order of oxidising power: F2 > Cl2 > Br2 > I2.
Reducing Power Increases Down the Group
• Increased shielding offsets increased nuclear charge, so the major variant is the distance between the
outermost electron and the nucleus.
• This distance increases, so the attraction between the outermost electron and the nucleus decreases.
• Hence it is easier for a halide ion to lose an electron from its outer shell and reduce another atom.
Cl- (aq)
N/A No Reaction No Reaction
(colourless)
Br- (aq) Cl2 + 2Br- → 2Cl- + Br2
N/A No Reaction
(colourless) Orange solution forms
I- (aq) Cl2 + 2I- → 2Cl- + I2 Br2 + 2I- → 2Br- + I2
N/A
(colourless) Brown solution forms Brown solution forms
7
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