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Comprehensive Chemistry Revision Notes
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@vi0me
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Atomic Structure and Subatomic Particles
Think of an atom as the smallest piece of an element that still acts like that element - it's literally the foundation of everything you can touch! Inside every atom, you'll find three main subatomic particles that work together like a perfectly balanced team.
The nucleus sits at the atom's centre, packed with protons and neutrons . Meanwhile, electrons (negative charge, almost no mass) whizz around the nucleus in shells. Here's the clever bit: atoms always have equal numbers of protons and electrons, making them electrically neutral overall.
Every atom gets two important numbers that tell its story. The atomic number shows how many protons it has (like an element's ID card), whilst the mass number counts all the protons and neutrons together. For example, potassium has 19 protons and a mass number of 39.
Quick Tip: Remember that nearly all an atom's mass comes from the nucleus - electrons are roughly 1,840 times lighter than protons!
Isotopes and Relative Atomic Mass
Here's where atoms get interesting - isotopes are like different versions of the same element! They have identical numbers of protons (same element) but different numbers of neutrons, giving them different masses. It's like having the same car model but with different engine sizes.
Hydrogen-1 is the most common isotope of hydrogen, whilst carbon has several isotopes including carbon-12. The name always tells you the mass number - dead simple! Since electrons determine chemical properties, isotopes of the same element react identically despite having different masses.
Relative atomic mass is basically a weighted average that accounts for all an element's isotopes and their natural abundance. You'll find these values on the periodic table with the symbol Ar. The formula is: (sum of isotope abundance × isotope mass number) ÷ (sum of all abundances).
Key Point: Mass numbers are always whole numbers, but relative atomic masses often aren't because they're averages of different isotopes!
The Periodic Table and Atomic Models
Mendeleev's periodic table was brilliant for its time - he arranged elements by increasing relative atomic mass and spotted repeating patterns (periodicity). He even left gaps for undiscovered elements and predicted their properties! The only hiccup was tellurium and iodine, which he had to swap based on their chemical properties rather than mass.
Today's modern periodic table arranges elements by atomic number (number of protons) rather than mass, solving Mendeleev's tellurium-iodine problem. Metals live on the left, non-metals on the right, with horizontal rows called periods and vertical columns called groups.
The journey from plum pudding model (1897) to nuclear atom was revolutionary. Rutherford's gold foil experiment (1905) showed that atoms are mostly empty space with a tiny, dense, positive nucleus. When alpha particles bounced back, it proved the nucleus was incredibly small but contained all the positive charge and most of the mass.
Bohr's model (1913) suggested electrons orbit in specific energy levels, explaining why different elements produce distinct flame colours. When electrons absorb energy, they jump to higher levels, then release light of definite frequencies when dropping back down.
Remember: The nucleus is about 1/10,000th the size of the whole atom - imagine a marble in a football stadium!
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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
Comprehensive Chemistry Revision Notes
vi
@vi0me
Ever wondered what makes up everything around you? Atoms are the tiny building blocks of all matter, and understanding their structure is key to mastering chemistry. From discovering subatomic particles to organising the periodic table, you'll learn how scientists unlocked... Show more
Atomic Structure and Subatomic Particles
Think of an atom as the smallest piece of an element that still acts like that element - it's literally the foundation of everything you can touch! Inside every atom, you'll find three main subatomic particles that work together like a perfectly balanced team.
The nucleus sits at the atom's centre, packed with protons and neutrons . Meanwhile, electrons (negative charge, almost no mass) whizz around the nucleus in shells. Here's the clever bit: atoms always have equal numbers of protons and electrons, making them electrically neutral overall.
Every atom gets two important numbers that tell its story. The atomic number shows how many protons it has (like an element's ID card), whilst the mass number counts all the protons and neutrons together. For example, potassium has 19 protons and a mass number of 39.
Quick Tip: Remember that nearly all an atom's mass comes from the nucleus - electrons are roughly 1,840 times lighter than protons!
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Improve your grades
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Isotopes and Relative Atomic Mass
Here's where atoms get interesting - isotopes are like different versions of the same element! They have identical numbers of protons (same element) but different numbers of neutrons, giving them different masses. It's like having the same car model but with different engine sizes.
Hydrogen-1 is the most common isotope of hydrogen, whilst carbon has several isotopes including carbon-12. The name always tells you the mass number - dead simple! Since electrons determine chemical properties, isotopes of the same element react identically despite having different masses.
Relative atomic mass is basically a weighted average that accounts for all an element's isotopes and their natural abundance. You'll find these values on the periodic table with the symbol Ar. The formula is: (sum of isotope abundance × isotope mass number) ÷ (sum of all abundances).
Key Point: Mass numbers are always whole numbers, but relative atomic masses often aren't because they're averages of different isotopes!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The Periodic Table and Atomic Models
Mendeleev's periodic table was brilliant for its time - he arranged elements by increasing relative atomic mass and spotted repeating patterns (periodicity). He even left gaps for undiscovered elements and predicted their properties! The only hiccup was tellurium and iodine, which he had to swap based on their chemical properties rather than mass.
Today's modern periodic table arranges elements by atomic number (number of protons) rather than mass, solving Mendeleev's tellurium-iodine problem. Metals live on the left, non-metals on the right, with horizontal rows called periods and vertical columns called groups.
The journey from plum pudding model (1897) to nuclear atom was revolutionary. Rutherford's gold foil experiment (1905) showed that atoms are mostly empty space with a tiny, dense, positive nucleus. When alpha particles bounced back, it proved the nucleus was incredibly small but contained all the positive charge and most of the mass.
Bohr's model (1913) suggested electrons orbit in specific energy levels, explaining why different elements produce distinct flame colours. When electrons absorb energy, they jump to higher levels, then release light of definite frequencies when dropping back down.
Remember: The nucleus is about 1/10,000th the size of the whole atom - imagine a marble in a football stadium!
We thought you’d never ask...
What is the Knowunity AI companion?
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.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
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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4.9/5
App Store
4.8/5
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