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4 Dec 2025
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Comprehensive Atomic Structure Notes for GCSE Chemistry
raniya
@raniya
1 / 3
Atomic Structure Basics
Think of an atom like a tiny solar system - there's a dense centre called the nucleus with particles called protons and neutrons packed inside. Around this nucleus, electrons zoom about in invisible paths called shells.
These three particles have different properties that make atoms work. Protons carry a positive charge (+1), neutrons have no charge (0), and electrons are negatively charged (-1). Protons and neutrons are roughly the same size, but electrons are absolutely tiny - about 1/1840th the mass of a proton!
Here's the clever bit: atoms are electrically neutral because they have equal numbers of protons and electrons. The positive and negative charges cancel each other out perfectly.
Quick Tip: Remember that atomic number = number of protons, and mass number = protons + neutrons. To find neutrons, just subtract atomic number from mass number!
Electronic Configuration
Now let's see how those electrons arrange themselves around the nucleus. They don't just float randomly - they occupy specific electron shells at different distances from the centre.
The shells fill up in a particular order with set limits. The first shell (closest to the nucleus) can only hold 2 electrons maximum. The second and third shells can each hold up to 8 electrons.
Take sodium as an example - it has an atomic number of 11, so it has 11 electrons. These arrange as 2 in the first shell, 8 in the second, and 1 in the third. We write this as 2, 8, 1 - much easier than drawing the whole atom!
Remember: Electrons always fill the innermost shells first before moving to outer ones - just like filling up the bottom floor of a building before the top!
Historical Models of the Atom
Scientists didn't always know what atoms looked like - they had to piece together clues over many years. Each discovery led to better atomic models that explained the evidence.
Thomson's Plum Pudding Model (1904) imagined the atom as a sphere of positive charge with negative electrons dotted throughout, like raisins in a pudding. It seemed reasonable at the time, but later experiments proved it wrong.
Rutherford's Model (1911) was a game-changer. Through clever experiments, he discovered that atoms have a tiny, dense, positively charged nucleus at the centre, with electrons moving around it in the empty space.
The final piece came when James Chadwick discovered neutrons in 1932. These were tricky to find because they have no electrical charge, but they explained why atomic masses didn't match up with just protons and electrons.
Did You Know? Rutherford's famous gold foil experiment showed that atoms are mostly empty space - if an atom were the size of a football stadium, the nucleus would be like a marble at the centre!
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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
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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
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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 😍😁😲🤑💗✨🎀😮
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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
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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
Comprehensive Atomic Structure Notes for GCSE Chemistry
raniya
@raniya
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. Let's explore how these invisible particles are put together and how scientists figured it... Show more
Atomic Structure Basics
Think of an atom like a tiny solar system - there's a dense centre called the nucleus with particles called protons and neutrons packed inside. Around this nucleus, electrons zoom about in invisible paths called shells.
These three particles have different properties that make atoms work. Protons carry a positive charge (+1), neutrons have no charge (0), and electrons are negatively charged (-1). Protons and neutrons are roughly the same size, but electrons are absolutely tiny - about 1/1840th the mass of a proton!
Here's the clever bit: atoms are electrically neutral because they have equal numbers of protons and electrons. The positive and negative charges cancel each other out perfectly.
Quick Tip: Remember that atomic number = number of protons, and mass number = protons + neutrons. To find neutrons, just subtract atomic number from mass number!
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Electronic Configuration
Now let's see how those electrons arrange themselves around the nucleus. They don't just float randomly - they occupy specific electron shells at different distances from the centre.
The shells fill up in a particular order with set limits. The first shell (closest to the nucleus) can only hold 2 electrons maximum. The second and third shells can each hold up to 8 electrons.
Take sodium as an example - it has an atomic number of 11, so it has 11 electrons. These arrange as 2 in the first shell, 8 in the second, and 1 in the third. We write this as 2, 8, 1 - much easier than drawing the whole atom!
Remember: Electrons always fill the innermost shells first before moving to outer ones - just like filling up the bottom floor of a building before the top!
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Historical Models of the Atom
Scientists didn't always know what atoms looked like - they had to piece together clues over many years. Each discovery led to better atomic models that explained the evidence.
Thomson's Plum Pudding Model (1904) imagined the atom as a sphere of positive charge with negative electrons dotted throughout, like raisins in a pudding. It seemed reasonable at the time, but later experiments proved it wrong.
Rutherford's Model (1911) was a game-changer. Through clever experiments, he discovered that atoms have a tiny, dense, positively charged nucleus at the centre, with electrons moving around it in the empty space.
The final piece came when James Chadwick discovered neutrons in 1932. These were tricky to find because they have no electrical charge, but they explained why atomic masses didn't match up with just protons and electrons.
Did You Know? Rutherford's famous gold foil experiment showed that atoms are mostly empty space - if an atom were the size of a football stadium, the nucleus would be like a marble at the centre!
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What is the Knowunity AI companion?
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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