Redox reactions and Group 7 chemistry are fundamental topics that...
Chemistry95 views·Updated 25 Aug 2026·3 pagesComprehensive AQA Chemistry Notes on Redox
Isabelle @isabelle_study
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1
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Redox Reactions and Oxidation States
Redox reactions are everywhere in chemistry, and they're easier to understand than you might think. Oxidation means losing electrons (or gaining oxygen), whilst reduction means gaining electrons (or losing oxygen). Remember: "OIL RIG" - Oxidation Is Loss, Reduction Is Gain.
Oxidising agents accept electrons and get reduced themselves, while reducing agents donate electrons and get oxidised. Sometimes you'll see disproportionation reactions where the same element is both oxidised and reduced simultaneously.
Oxidation states help you track electron movement in compounds. Elements alone have an oxidation state of zero, but in compounds they show how many electrons are needed to reach zero. Group 1 metals are always +1, Group 2 are +2, oxygen is usually -2, and hydrogen is typically +1.
Quick Tip: When writing half equations, follow the steps: balance the main atom, add H₂O, add H⁺, then add electrons. This systematic approach works every time!
2
of 3
Group 7 Trends and Oxidising Power
Group 7 elements (the halogens) show clear trends that make perfect sense once you understand the underlying reasons. As you go down the group, electronegativity and ionisation energy decrease, whilst atomic radius and boiling point increase.
These trends happen because each element has an extra electron shell, creating more shielding. This means outer electrons are further from the nucleus and experience less attraction. More electrons also create stronger Van der Waals forces, explaining the higher boiling points.
Oxidising power decreases down Group 7, which you can see through displacement reactions. Chlorine displaces bromine from bromide solutions (turning them orange), and bromine displaces iodine from iodide solutions (creating dark brown solutions).
Remember: More reactive halogens will always displace less reactive ones from their compounds - it's like a chemical hierarchy!
3
of 3
Reducing Power of Halides with Concentrated Sulphuric Acid
The reducing power of halide ions increases as you go down Group 7, and this becomes obvious when they react with concentrated sulphuric acid. Fluoride and chloride ions are weak reducing agents that only do simple acid-base reactions, producing misty white fumes of HF or HCl.
Bromide ions are stronger reducing agents and can actually reduce the sulphuric acid to sulphur dioxide (colourless gas), whilst also forming orange bromine fumes. The reaction produces both the expected HBr and the reduction products.
Iodide ions are the strongest reducing agents of all the halides. They can reduce sulphuric acid to multiple products: sulphur dioxide (colourless gas), sulphur (yellow solid), or even hydrogen sulphide (bad egg smell). You'll see purple iodine fumes or black solid iodine forming alongside these reduction products.
Key Point: The more you go down Group 7, the better the halide ions become at reducing other substances - iodide is the champion reducer!
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Chemistry95 views·Updated 25 Aug 2026·3 pagesComprehensive AQA Chemistry Notes on Redox
Isabelle @isabelle_study
Redox reactions and Group 7 chemistry are fundamental topics that explain how electrons transfer between substances and how halogens behave. Understanding these concepts will help you tackle chemical equations, predict reactions, and explain the trends you see across the periodic...
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Redox Reactions and Oxidation States
Redox reactions are everywhere in chemistry, and they're easier to understand than you might think. Oxidation means losing electrons (or gaining oxygen), whilst reduction means gaining electrons (or losing oxygen). Remember: "OIL RIG" - Oxidation Is Loss, Reduction Is Gain.
Oxidising agents accept electrons and get reduced themselves, while reducing agents donate electrons and get oxidised. Sometimes you'll see disproportionation reactions where the same element is both oxidised and reduced simultaneously.
Oxidation states help you track electron movement in compounds. Elements alone have an oxidation state of zero, but in compounds they show how many electrons are needed to reach zero. Group 1 metals are always +1, Group 2 are +2, oxygen is usually -2, and hydrogen is typically +1.
Quick Tip: When writing half equations, follow the steps: balance the main atom, add H₂O, add H⁺, then add electrons. This systematic approach works every time!
2
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Group 7 Trends and Oxidising Power
Group 7 elements (the halogens) show clear trends that make perfect sense once you understand the underlying reasons. As you go down the group, electronegativity and ionisation energy decrease, whilst atomic radius and boiling point increase.
These trends happen because each element has an extra electron shell, creating more shielding. This means outer electrons are further from the nucleus and experience less attraction. More electrons also create stronger Van der Waals forces, explaining the higher boiling points.
Oxidising power decreases down Group 7, which you can see through displacement reactions. Chlorine displaces bromine from bromide solutions (turning them orange), and bromine displaces iodine from iodide solutions (creating dark brown solutions).
Remember: More reactive halogens will always displace less reactive ones from their compounds - it's like a chemical hierarchy!
3
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Reducing Power of Halides with Concentrated Sulphuric Acid
The reducing power of halide ions increases as you go down Group 7, and this becomes obvious when they react with concentrated sulphuric acid. Fluoride and chloride ions are weak reducing agents that only do simple acid-base reactions, producing misty white fumes of HF or HCl.
Bromide ions are stronger reducing agents and can actually reduce the sulphuric acid to sulphur dioxide (colourless gas), whilst also forming orange bromine fumes. The reaction produces both the expected HBr and the reduction products.
Iodide ions are the strongest reducing agents of all the halides. They can reduce sulphuric acid to multiple products: sulphur dioxide (colourless gas), sulphur (yellow solid), or even hydrogen sulphide (bad egg smell). You'll see purple iodine fumes or black solid iodine forming alongside these reduction products.
Key Point: The more you go down Group 7, the better the halide ions become at reducing other substances - iodide is the champion reducer!
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