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
5 Dec 2025
189
3 pages
mkxxx_ @mk___
Understanding atomic structure and the periodic table is crucial for mastering chemistry - and it's actually way more... Show more
Ever wondered what everything around you is actually made of? Atoms are the tiny building blocks of all matter - they're the smallest part of an element that can still exist. Each element has its own chemical symbol (like O for oxygen), making chemistry like a giant alphabet!
Here's where it gets interesting compounds contain two or more elements chemically stuck together, whilst mixtures are just elements hanging out together without actually bonding. You can separate mixtures using physical methods like filtration or distillation - think of it like sorting your laundry!
The journey to understand atoms started with scientists thinking they were just tiny, solid spheres. Then J.J. Thompson discovered electrons and created the plum pudding model - imagine a ball of positive charge with negative electrons dotted throughout like raisins in a pudding.
Key Point The famous alpha-scattering experiment with gold foil completely changed our understanding of atomic structure!
The alpha-scattering experiment was brilliant scientists fired positively charged particles at super-thin gold foil. Most went straight through (showing atoms are mostly empty space), some bounced off at angles, and a few bounced straight back! This proved that atoms have a dense, positively charged centre called the nucleus, leading to our modern nuclear model with electrons orbiting around it.
Right, let's get to grips with what's actually inside atoms. You've got three main players protons , neutrons , and electrons . The protons and neutrons hang out in the nucleus, whilst electrons zoom around in shells.
Isotopes are atoms of the same element with different numbers of neutrons - they're like identical twins with different weights! The relative atomic mass tells you the average mass of an element's atoms, and there's a handy formula to calculate it using isotope abundances.
The periodic table is basically chemistry's best organisational system. Elements are arranged by atomic number (number of protons), and here's the clever bit elements in the same group (column) have the same number of outer electrons, giving them similar properties.
Historical Note Mendeleev was so confident in his periodic table that he predicted undiscovered elements - and he was right!
The table's history is fascinating too. Dobereiner noticed elements came in threes with similar properties, Newlands spotted patterns every eighth element, but Mendeleev cracked it properly. He arranged elements by atomic weight but wasn't afraid to swap things around or leave gaps for undiscovered elements. When those elements were found years later with exactly the properties he predicted, everyone knew he'd nailed it!
Drawing an imaginary line down the periodic table splits it into two very different neighbourhoods. Metals live on the left side and are generally hard, shiny, and brilliant at conducting heat and electricity. Non-metals occupy the right side and are typically brittle, dull, and rubbish conductors (except graphite, which breaks the rules).
Think about it practically metals are perfect for making machinery and electrical wires because they're strong and conductive. Non-metals are more useful in medicine and chemical reactions because of their different properties. Copper wires and carbon-based medicines are perfect examples of each doing what they do best.
Group 0 elements (the noble gases) are the chemistry world's introverts - they're completely unreactive because they have full outer electron shells. They're perfectly content and don't want to react with anyone else!
Pattern Spotting As you go down Group 0, the boiling points increase - helium boils at -269°C whilst radon boils at -62°C.
There's a lovely pattern in Group 0 as the relative atomic mass increases going down the group, so does the boiling point. It's like the heavier noble gases need more energy to escape from liquid to gas. These patterns make the periodic table incredibly useful for predicting properties of elements you've never encountered before!
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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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
mkxxx_
@mk___
Understanding atomic structure and the periodic table is crucial for mastering chemistry - and it's actually way more fascinating than you might think! This revision guide covers the journey from early atomic models to the modern periodic table, showing how... Show more
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Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ever wondered what everything around you is actually made of? Atoms are the tiny building blocks of all matter - they're the smallest part of an element that can still exist. Each element has its own chemical symbol (like O for oxygen), making chemistry like a giant alphabet!
Here's where it gets interesting: compounds contain two or more elements chemically stuck together, whilst mixtures are just elements hanging out together without actually bonding. You can separate mixtures using physical methods like filtration or distillation - think of it like sorting your laundry!
The journey to understand atoms started with scientists thinking they were just tiny, solid spheres. Then J.J. Thompson discovered electrons and created the plum pudding model - imagine a ball of positive charge with negative electrons dotted throughout like raisins in a pudding.
Key Point: The famous alpha-scattering experiment with gold foil completely changed our understanding of atomic structure!
The alpha-scattering experiment was brilliant: scientists fired positively charged particles at super-thin gold foil. Most went straight through (showing atoms are mostly empty space), some bounced off at angles, and a few bounced straight back! This proved that atoms have a dense, positively charged centre called the nucleus, leading to our modern nuclear model with electrons orbiting around it.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Right, let's get to grips with what's actually inside atoms. You've got three main players: protons , neutrons , and electrons . The protons and neutrons hang out in the nucleus, whilst electrons zoom around in shells.
Isotopes are atoms of the same element with different numbers of neutrons - they're like identical twins with different weights! The relative atomic mass tells you the average mass of an element's atoms, and there's a handy formula to calculate it using isotope abundances.
The periodic table is basically chemistry's best organisational system. Elements are arranged by atomic number (number of protons), and here's the clever bit: elements in the same group (column) have the same number of outer electrons, giving them similar properties.
Historical Note: Mendeleev was so confident in his periodic table that he predicted undiscovered elements - and he was right!
The table's history is fascinating too. Dobereiner noticed elements came in threes with similar properties, Newlands spotted patterns every eighth element, but Mendeleev cracked it properly. He arranged elements by atomic weight but wasn't afraid to swap things around or leave gaps for undiscovered elements. When those elements were found years later with exactly the properties he predicted, everyone knew he'd nailed it!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Drawing an imaginary line down the periodic table splits it into two very different neighbourhoods. Metals live on the left side and are generally hard, shiny, and brilliant at conducting heat and electricity. Non-metals occupy the right side and are typically brittle, dull, and rubbish conductors (except graphite, which breaks the rules).
Think about it practically: metals are perfect for making machinery and electrical wires because they're strong and conductive. Non-metals are more useful in medicine and chemical reactions because of their different properties. Copper wires and carbon-based medicines are perfect examples of each doing what they do best.
Group 0 elements (the noble gases) are the chemistry world's introverts - they're completely unreactive because they have full outer electron shells. They're perfectly content and don't want to react with anyone else!
Pattern Spotting: As you go down Group 0, the boiling points increase - helium boils at -269°C whilst radon boils at -62°C.
There's a lovely pattern in Group 0: as the relative atomic mass increases going down the group, so does the boiling point. It's like the heavier noble gases need more energy to escape from liquid to gas. These patterns make the periodic table incredibly useful for predicting properties of elements you've never encountered before!
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.
2
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