Subjects
Maths
Chemistry
Biology
English Language
History
Responding to change (a2 only)
Infection and response
Homeostasis and response
Energy transfers (a2 only)
Cell biology
Organisms respond to changes in their internal and external environments (a-level only)
Biological molecules
Organisation
Substance exchange
Bioenergetics
Genetic information & variation
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
Cells
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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
World war one
Britain: 1509 -1745
Show all topics
Chemistry
5 Dec 2025
661
4 pages
paige gibbs @paigegibbs_vuvr
Chemistry's all about understanding how substances behave, from the acids in your stomach to the metals in your... Show more
Ever wondered why lemon juice stings cuts or why soap feels slippery? It's all about acids and bases. Acids have a pH less than 7 and release hydrogen ions in water - think stomach acid (pH 2) or acid rain (pH 4). Bases have a pH greater than 7 and form hydroxide ions in water, like washing up liquid (pH 9) or bleach (pH 13).
The pH scale runs from 1-14 and measures hydrogen ion concentration. A pH of 7 is neutral (pure water), whilst anything below is acidic and anything above is alkaline. You can measure pH using indicators (chemical dyes that change colour) or a pH meter for more accurate results.
When acids and bases meet, they have a neutralisation reaction acid + base → salt + water. For example, HCl + NaOH → NaCl + H2O. The key reaction is H+ + OH- → H2O, which is why the solution becomes neutral.
Quick Tip Don't confuse acid strength (how much it breaks apart) with concentration (how much acid is in a given volume) - they're completely different things!
Your understanding of atoms has come a long way since ancient Greece! Democritus (500 BC) first suggested everything was made of tiny, unbreakable particles. Much later, John Dalton (1803) proposed atoms were solid spheres - different elements had different types of spheres.
JJ Thompson (1897) discovered electrons and created the plum pudding model - a positive ball with negative electrons dotted throughout. However, Ernest Rutherford's gold foil experiment (1909) changed everything when some particles bounced back, proving atoms had a dense, positive nucleus with electrons around it.
Niels Bohr (1913) refined this into the electron shell model, showing electrons orbit the nucleus in specific shells. Finally, James Chadwick discovered neutrons in the 1930s, completing our modern picture of atoms with protons and neutrons in the nucleus, and electrons in shells.
Remember Each scientist built on previous work - science is about testing and improving ideas, not getting everything right first time!
Atoms bond in three main ways, and understanding these explains why materials behave so differently. Ionic bonding happens between metals and non-metals - metals lose electrons to become positive ions, non-metals gain them to become negative ions. The strong electrostatic attraction between oppositely charged ions creates the bond.
Covalent bonding occurs between non-metals that share electron pairs. This creates either small molecules (like water H₂O) with weak forces between molecules, or giant covalent structures like diamond and silicon dioxide. Diamond's incredibly hard because every carbon atom bonds to four others in a rigid 3D network.
Metallic bonding explains why metals conduct electricity and can be hammered into shape. Metal atoms release electrons into a "sea" of delocalised electrons, creating positive ions held together by attraction to these mobile electrons. The layers can slide over each other, making metals malleable.
Key Insight The type of bonding determines a material's properties - ionic compounds have high melting points, small molecules are often gases, and metals conduct electricity.
Carbon's versatility creates some amazing materials beyond diamond. Graphite has a layered structure where each carbon bonds to three others, leaving one electron delocalised. This makes graphite soft (layers slide easily) and electrically conductive - perfect for pencils and electrodes.
Graphene is essentially a single layer of graphite arranged in hexagons - it's incredibly strong, nearly transparent, and conducts heat and electricity brilliantly. Fullerenes are hollow carbon structures like cages, tubes, and balls. The most famous is buckminsterfullerene (C₆₀), which looks like a football and has potential uses in drug delivery and nanotechnology.
Metallic bonding also explains alloys - mixtures containing at least one metal. Steel (iron with carbon) is stronger than pure iron because the different-sized atoms disrupt the regular arrangement, preventing layers from sliding easily. This gives alloys improved properties like increased strength.
Polymers are large molecules made from repeating units held by strong covalent bonds. They're typically solid at room temperature, cheap to produce, and incredibly versatile - forming everything from plastic bottles to synthetic fibres.
Cool Fact Fullerenes have an incredibly high strength-to-weight ratio, making them perfect for reinforcing materials in everything from tennis rackets to spacecraft!
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.
11
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
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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
paige gibbs
@paigegibbs_vuvr
Chemistry's all about understanding how substances behave, from the acids in your stomach to the metals in your phone. This guide covers three essential topics: acids and bases (and how they interact), the fascinating history of atomic theory, and chemical... Show more
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Improve your grades
Join milions of students
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Ever wondered why lemon juice stings cuts or why soap feels slippery? It's all about acids and bases. Acids have a pH less than 7 and release hydrogen ions in water - think stomach acid (pH 2) or acid rain (pH 4). Bases have a pH greater than 7 and form hydroxide ions in water, like washing up liquid (pH 9) or bleach (pH 13).
The pH scale runs from 1-14 and measures hydrogen ion concentration. A pH of 7 is neutral (pure water), whilst anything below is acidic and anything above is alkaline. You can measure pH using indicators (chemical dyes that change colour) or a pH meter for more accurate results.
When acids and bases meet, they have a neutralisation reaction: acid + base → salt + water. For example, HCl + NaOH → NaCl + H2O. The key reaction is H+ + OH- → H2O, which is why the solution becomes neutral.
Quick Tip: Don't confuse acid strength (how much it breaks apart) with concentration (how much acid is in a given volume) - they're completely different things!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Your understanding of atoms has come a long way since ancient Greece! Democritus (500 BC) first suggested everything was made of tiny, unbreakable particles. Much later, John Dalton (1803) proposed atoms were solid spheres - different elements had different types of spheres.
JJ Thompson (1897) discovered electrons and created the plum pudding model - a positive ball with negative electrons dotted throughout. However, Ernest Rutherford's gold foil experiment (1909) changed everything when some particles bounced back, proving atoms had a dense, positive nucleus with electrons around it.
Niels Bohr (1913) refined this into the electron shell model, showing electrons orbit the nucleus in specific shells. Finally, James Chadwick discovered neutrons in the 1930s, completing our modern picture of atoms with protons and neutrons in the nucleus, and electrons in shells.
Remember: Each scientist built on previous work - science is about testing and improving ideas, not getting everything right first time!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Atoms bond in three main ways, and understanding these explains why materials behave so differently. Ionic bonding happens between metals and non-metals - metals lose electrons to become positive ions, non-metals gain them to become negative ions. The strong electrostatic attraction between oppositely charged ions creates the bond.
Covalent bonding occurs between non-metals that share electron pairs. This creates either small molecules (like water H₂O) with weak forces between molecules, or giant covalent structures like diamond and silicon dioxide. Diamond's incredibly hard because every carbon atom bonds to four others in a rigid 3D network.
Metallic bonding explains why metals conduct electricity and can be hammered into shape. Metal atoms release electrons into a "sea" of delocalised electrons, creating positive ions held together by attraction to these mobile electrons. The layers can slide over each other, making metals malleable.
Key Insight: The type of bonding determines a material's properties - ionic compounds have high melting points, small molecules are often gases, and metals conduct electricity.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Carbon's versatility creates some amazing materials beyond diamond. Graphite has a layered structure where each carbon bonds to three others, leaving one electron delocalised. This makes graphite soft (layers slide easily) and electrically conductive - perfect for pencils and electrodes.
Graphene is essentially a single layer of graphite arranged in hexagons - it's incredibly strong, nearly transparent, and conducts heat and electricity brilliantly. Fullerenes are hollow carbon structures like cages, tubes, and balls. The most famous is buckminsterfullerene (C₆₀), which looks like a football and has potential uses in drug delivery and nanotechnology.
Metallic bonding also explains alloys - mixtures containing at least one metal. Steel (iron with carbon) is stronger than pure iron because the different-sized atoms disrupt the regular arrangement, preventing layers from sliding easily. This gives alloys improved properties like increased strength.
Polymers are large molecules made from repeating units held by strong covalent bonds. They're typically solid at room temperature, cheap to produce, and incredibly versatile - forming everything from plastic bottles to synthetic fibres.
Cool Fact: Fullerenes have an incredibly high strength-to-weight ratio, making them perfect for reinforcing materials in everything from tennis rackets to spacecraft!
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.
11
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
App 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