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Britain & the wider world: 1745 -1901
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Chemistry
7 Dec 2025
58
3 pages
Isabelle @isabelle_study
Redox reactions and Group 7 chemistry are fundamental topics that explain how electrons transfer between substances and how... Show more
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!
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!
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!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the chemistry of carbonyl compounds, including the reduction of aldehydes and ketones to alcohols using NaBH4, oxidation processes, and the significance of functional groups. This summary covers key concepts such as nucleophilic addition, oxidation-reduction reactions, and the properties of carbonyl functional groups. Ideal for organic chemistry students seeking to understand the behavior of carbonyl compounds in various reactions.
ChemistryExplore the key reactions of alcohols, including combustion, substitution with halogens, dehydration to form alkenes, and oxidation to aldehydes and carboxylic acids. This summary covers essential tests for aldehydes and the reactivity of different alcohol types. Ideal for chemistry students preparing for exams.
ChemistryExplore key concepts in organic chemistry with this comprehensive overview. Covering functional groups, structural formulas, and reaction mechanisms, this resource is perfect for A-level students. Includes insights on alcohols, carboxylic acids, alkenes, and spectroscopy techniques. Ideal for exam preparation and understanding organic synthesis.
ChemistryExplore key organic reaction mechanisms including electrophilic addition, free radical substitution, and nucleophilic substitution. This summary covers hydrocarbons, alkanes, alkenes, and their transformations, essential for AQA AS Level organic chemistry. Ideal for students seeking to understand complex organic processes and improve exam performance.
ChemistryExplore the reactivity and reactions of alkenes and alcohols in organic chemistry. This summary covers key concepts such as addition reactions, oxidation processes, isomerism, and environmental impacts of organic compounds. Ideal for A Level Chemistry students preparing for exams. Key topics include electrophilic addition, Markovnikov's rule, and the distillation process.
ChemistryExplore the principles of electron configuration, including the Aufbau principle, Pauli exclusion principle, and Hund's rule. This summary covers the arrangement of electrons in atomic orbitals, subshell energy levels, and exceptions in electron configurations for elements like chromium and copper. Ideal for A Level Chemistry students seeking clarity on these fundamental concepts.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
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... Show more
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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!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
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!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
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!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
3
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the chemistry of carbonyl compounds, including the reduction of aldehydes and ketones to alcohols using NaBH4, oxidation processes, and the significance of functional groups. This summary covers key concepts such as nucleophilic addition, oxidation-reduction reactions, and the properties of carbonyl functional groups. Ideal for organic chemistry students seeking to understand the behavior of carbonyl compounds in various reactions.
ChemistryExplore the key reactions of alcohols, including combustion, substitution with halogens, dehydration to form alkenes, and oxidation to aldehydes and carboxylic acids. This summary covers essential tests for aldehydes and the reactivity of different alcohol types. Ideal for chemistry students preparing for exams.
ChemistryExplore key concepts in organic chemistry with this comprehensive overview. Covering functional groups, structural formulas, and reaction mechanisms, this resource is perfect for A-level students. Includes insights on alcohols, carboxylic acids, alkenes, and spectroscopy techniques. Ideal for exam preparation and understanding organic synthesis.
ChemistryExplore key organic reaction mechanisms including electrophilic addition, free radical substitution, and nucleophilic substitution. This summary covers hydrocarbons, alkanes, alkenes, and their transformations, essential for AQA AS Level organic chemistry. Ideal for students seeking to understand complex organic processes and improve exam performance.
ChemistryExplore the reactivity and reactions of alkenes and alcohols in organic chemistry. This summary covers key concepts such as addition reactions, oxidation processes, isomerism, and environmental impacts of organic compounds. Ideal for A Level Chemistry students preparing for exams. Key topics include electrophilic addition, Markovnikov's rule, and the distillation process.
ChemistryExplore the principles of electron configuration, including the Aufbau principle, Pauli exclusion principle, and Hund's rule. This summary covers the arrangement of electrons in atomic orbitals, subshell energy levels, and exceptions in electron configurations for elements like chromium and copper. Ideal for A Level Chemistry students seeking clarity on these fundamental concepts.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Sociology