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
Show all topics
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
746
•
29 Nov 2025
•
Mayesha ☆
@mayeshatas07
Understanding atoms and chemical reactions is like learning the secret... Show more
Think of atoms as the ultimate building blocks - they're literally what everything is made of. Each element on the periodic table gets its own symbol, like a chemical shorthand that scientists use worldwide.
Compounds form when two or more different atoms decide to chemically bond together, creating something completely new. During chemical reactions, atoms simply rearrange themselves - they never disappear or magically appear, which is why you need to balance equations.
Your understanding of atomic structure has evolved thanks to brilliant scientists over time. JJ Thompson started with the "plum pudding model," but Ernest Rutherford discovered that atoms actually have a tiny, dense nucleus at their centre. Neils Bohr then figured out that electrons orbit in specific shells, whilst James Chadwick identified neutrons hiding in the nucleus alongside protons.
Quick Tip: Remember that the atomic number tells you how many protons an element has, whilst the mass number is protons plus neutrons. Isotopes are just atoms with extra or fewer neutrons - same element, different weight!
The periodic table isn't random - it's organised by atomic number, and elements in the same group behave similarly because they have the same number of outer shell electrons. Metals (left side) love giving away electrons, whilst non-metals (right side) prefer collecting them.
Chemical bonding is basically atoms trying to achieve the perfect electron setup. Metals use metallic bonding, creating a sea of delocalised electrons that makes them great conductors. Non-metals prefer covalent bonding, sharing electrons like good friends.
When metals meet non-metals, you get ionic bonding - it's like a complete electron transfer where metals donate and non-metals accept. Ionic compounds are tough cookies with high melting points and can conduct electricity when dissolved, whilst molecular compounds are much more chill with low boiling points.
States of matter are all about particle arrangement and energy. Solids have particles packed tightly, liquids flow freely, and gases spread everywhere. Melting and boiling happen when you add enough energy to overcome the forces holding particles together.
Remember: Physical changes like melting don't create new substances - you're just changing the arrangement, not the identity!
Separation techniques are your toolkit for unmixing things. Filtration catches solid bits, crystallisation leaves behind dissolved solids, distillation separates liquids by their boiling points, and chromatography sorts substances by how fast they travel. Concentrations help you measure exactly how much stuff is dissolved in your solutions.
Chemical reactions transform reactants into products - it's like following a recipe where atoms rearrange themselves. Balanced equations are crucial because mass never disappears (conservation of mass), so you need equal numbers of each atom type on both sides.
Reversible reactions can reach equilibrium, where forward and reverse reactions happen at the same rate. Le Chatelier's principle is like a chemical balancing act - if you change conditions, the reaction shifts to counteract that change.
Percentage yield and atom economy measure how efficient your reactions are. Think of them as your chemistry report card - they tell you how much product you actually got versus how much you could theoretically make.
Pro Tip: Titrations are like chemical detective work - you use a solution of known concentration to figure out the concentration of an unknown acid or alkali!
Electrolysis uses electricity to split ionic compounds apart, which is brilliant for extracting or purifying metals. Corrosion like rusting happens when metals react with their environment, but alloys (metal mixtures) can help prevent this.
Environmental chemistry matters more than ever. Life cycle assessments consider everything from mining raw materials to disposing of waste, helping us make better choices about recycling and sustainable processes.
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.
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
Mayesha ☆
@mayeshatas07
Understanding atoms and chemical reactions is like learning the secret language of everything around you - from the water you drink to the phone in your pocket! This revision guide breaks down the essential concepts you need to master for... Show more
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Think of atoms as the ultimate building blocks - they're literally what everything is made of. Each element on the periodic table gets its own symbol, like a chemical shorthand that scientists use worldwide.
Compounds form when two or more different atoms decide to chemically bond together, creating something completely new. During chemical reactions, atoms simply rearrange themselves - they never disappear or magically appear, which is why you need to balance equations.
Your understanding of atomic structure has evolved thanks to brilliant scientists over time. JJ Thompson started with the "plum pudding model," but Ernest Rutherford discovered that atoms actually have a tiny, dense nucleus at their centre. Neils Bohr then figured out that electrons orbit in specific shells, whilst James Chadwick identified neutrons hiding in the nucleus alongside protons.
Quick Tip: Remember that the atomic number tells you how many protons an element has, whilst the mass number is protons plus neutrons. Isotopes are just atoms with extra or fewer neutrons - same element, different weight!
The periodic table isn't random - it's organised by atomic number, and elements in the same group behave similarly because they have the same number of outer shell electrons. Metals (left side) love giving away electrons, whilst non-metals (right side) prefer collecting them.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Chemical bonding is basically atoms trying to achieve the perfect electron setup. Metals use metallic bonding, creating a sea of delocalised electrons that makes them great conductors. Non-metals prefer covalent bonding, sharing electrons like good friends.
When metals meet non-metals, you get ionic bonding - it's like a complete electron transfer where metals donate and non-metals accept. Ionic compounds are tough cookies with high melting points and can conduct electricity when dissolved, whilst molecular compounds are much more chill with low boiling points.
States of matter are all about particle arrangement and energy. Solids have particles packed tightly, liquids flow freely, and gases spread everywhere. Melting and boiling happen when you add enough energy to overcome the forces holding particles together.
Remember: Physical changes like melting don't create new substances - you're just changing the arrangement, not the identity!
Separation techniques are your toolkit for unmixing things. Filtration catches solid bits, crystallisation leaves behind dissolved solids, distillation separates liquids by their boiling points, and chromatography sorts substances by how fast they travel. Concentrations help you measure exactly how much stuff is dissolved in your solutions.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Chemical reactions transform reactants into products - it's like following a recipe where atoms rearrange themselves. Balanced equations are crucial because mass never disappears (conservation of mass), so you need equal numbers of each atom type on both sides.
Reversible reactions can reach equilibrium, where forward and reverse reactions happen at the same rate. Le Chatelier's principle is like a chemical balancing act - if you change conditions, the reaction shifts to counteract that change.
Percentage yield and atom economy measure how efficient your reactions are. Think of them as your chemistry report card - they tell you how much product you actually got versus how much you could theoretically make.
Pro Tip: Titrations are like chemical detective work - you use a solution of known concentration to figure out the concentration of an unknown acid or alkali!
Electrolysis uses electricity to split ionic compounds apart, which is brilliant for extracting or purifying metals. Corrosion like rusting happens when metals react with their environment, but alloys (metal mixtures) can help prevent this.
Environmental chemistry matters more than ever. Life cycle assessments consider everything from mining raw materials to disposing of waste, helping us make better choices about recycling and sustainable processes.
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
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
