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
Chemistry
10 Dec 2025
125
2 pages
Anna Rusin @annarusin_cghn
The atom's story is a fascinating journey of scientific discovery. Over the centuries, our understanding of atomic structure... Show more
Ever wondered how scientists figured out what atoms look like? It's been quite the adventure! In the early 19th century, John Dalton simply described atoms as solid spheres that made up different elements. Pretty basic, right?
Everything changed in 1897 when JJ Thomson discovered electrons. His experiments proved atoms weren't solid after all but contained smaller, negatively charged particles. This led to the famous plum pudding model - imagine a positively charged ball with electrons stuck inside it like fruit in a pudding.
Then came Ernest Rutherford's game-changing experiment in 1909. He fired positively charged alpha particles at thin gold foil, expecting them to pass straight through based on Thomson's model. Surprisingly, some particles bounced back! This led to Rutherford's nuclear model - a tiny, dense, positively charged nucleus at the center with electrons orbiting in the mostly empty space around it.
Did you know? Rutherford's gold foil experiment is one of the most famous in scientific history. He later said that seeing particles bounce back was "as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!"
Niels Bohr improved on this model by suggesting electrons orbit in specific shells or energy levels around the nucleus. This solved a major problem with Rutherford's model - according to physics at that time, electrons would quickly spiral into the nucleus. Bohr's model was supported by experimental evidence and helped explain many scientific observations of the period.
The story of the atom doesn't end with Rutherford and Bohr! Further experiments revealed even more fascinating details about the nucleus itself.
Rutherford and his colleagues continued investigating and discovered that the nucleus contains smaller particles with the same charge as a hydrogen nucleus. These positively charged particles became known as protons. This was another huge step forward in understanding atomic structure.
About 20 years later, James Chadwick made the final major discovery needed to complete our basic understanding of atoms. Through clever experiments, he provided evidence for neutral particles (with no charge) in the nucleus, which we now call neutrons.
The discovery of neutrons gave us the nuclear model of the atom that's still accepted today - a central nucleus containing protons and neutrons, surrounded by electrons in shells. This model has stood the test of time and forms the foundation of our understanding of chemistry and physics.
Think about it The entire journey from "atoms are solid spheres" to our modern understanding took just over a century. Imagine what discoveries about atomic structure might happen in your lifetime!
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.
6
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the key developments in atomic theory from Democritus to Maria Goeppert-Mayer. This timeline highlights significant contributions to our understanding of atomic structure, including the discovery of protons, neutrons, and electrons, and the evolution of atomic models. Ideal for students studying atomic theory and its historical context.
ChemistryExplore the concept of internal energy, including the roles of kinetic and potential energy in particles, the effects of heating on temperature and state changes, and the significance of specific latent heat in phase transitions. This summary covers key principles such as energy transfer, latent heat of fusion, and vaporization, essential for mastering thermodynamics.
Combined ScienceExplore the principles of heat transfer through conduction, convection, and radiation. This summary covers key concepts such as thermal conductivity, insulators vs. conductors, and the role of temperature in energy transfers. Ideal for students studying the structure of matter and phase changes.
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
Anna Rusin
@annarusin_cghn
The atom's story is a fascinating journey of scientific discovery. Over the centuries, our understanding of atomic structure has dramatically evolved through groundbreaking experiments and bold new theories. Let's explore how our view of this fundamental building block of matter... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ever wondered how scientists figured out what atoms look like? It's been quite the adventure! In the early 19th century, John Dalton simply described atoms as solid spheres that made up different elements. Pretty basic, right?
Everything changed in 1897 when JJ Thomson discovered electrons. His experiments proved atoms weren't solid after all but contained smaller, negatively charged particles. This led to the famous plum pudding model - imagine a positively charged ball with electrons stuck inside it like fruit in a pudding.
Then came Ernest Rutherford's game-changing experiment in 1909. He fired positively charged alpha particles at thin gold foil, expecting them to pass straight through based on Thomson's model. Surprisingly, some particles bounced back! This led to Rutherford's nuclear model - a tiny, dense, positively charged nucleus at the center with electrons orbiting in the mostly empty space around it.
Did you know? Rutherford's gold foil experiment is one of the most famous in scientific history. He later said that seeing particles bounce back was "as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!"
Niels Bohr improved on this model by suggesting electrons orbit in specific shells or energy levels around the nucleus. This solved a major problem with Rutherford's model - according to physics at that time, electrons would quickly spiral into the nucleus. Bohr's model was supported by experimental evidence and helped explain many scientific observations of the period.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The story of the atom doesn't end with Rutherford and Bohr! Further experiments revealed even more fascinating details about the nucleus itself.
Rutherford and his colleagues continued investigating and discovered that the nucleus contains smaller particles with the same charge as a hydrogen nucleus. These positively charged particles became known as protons. This was another huge step forward in understanding atomic structure.
About 20 years later, James Chadwick made the final major discovery needed to complete our basic understanding of atoms. Through clever experiments, he provided evidence for neutral particles (with no charge) in the nucleus, which we now call neutrons.
The discovery of neutrons gave us the nuclear model of the atom that's still accepted today - a central nucleus containing protons and neutrons, surrounded by electrons in shells. This model has stood the test of time and forms the foundation of our understanding of chemistry and physics.
Think about it: The entire journey from "atoms are solid spheres" to our modern understanding took just over a century. Imagine what discoveries about atomic structure might happen in your lifetime!
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.
6
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the key developments in atomic theory from Democritus to Maria Goeppert-Mayer. This timeline highlights significant contributions to our understanding of atomic structure, including the discovery of protons, neutrons, and electrons, and the evolution of atomic models. Ideal for students studying atomic theory and its historical context.
ChemistryExplore the concept of internal energy, including the roles of kinetic and potential energy in particles, the effects of heating on temperature and state changes, and the significance of specific latent heat in phase transitions. This summary covers key principles such as energy transfer, latent heat of fusion, and vaporization, essential for mastering thermodynamics.
Combined ScienceExplore the principles of heat transfer through conduction, convection, and radiation. This summary covers key concepts such as thermal conductivity, insulators vs. conductors, and the role of temperature in energy transfers. Ideal for students studying the structure of matter and phase changes.
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