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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
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Chemistry
10 Dec 2025
206
1 page
Imogen @iimogen.
Atomic structure might seem complex, but it's actually the foundation that explains how everything around you works. From... Show more
Ever wondered how scientists figure out the exact mass of atoms? Relative Atomic Mass (RAM) compares an atom's mass to 1/12 of a carbon-12 atom's mass. When you're dealing with isotopes (atoms with different numbers of neutrons), you calculate RAM using a weighted average.
Here's a quick example if copper has 50.1% Cu-63 and 49.9% Cu-65, you'd calculate (50.1×63 + 49.9×65) ÷ 100 = 63.50. The percentages act as weights because they show how common each isotope is in nature.
Mass spectrometry is the tool that makes these measurements possible. It works by accelerating ionised samples through a flight path - heavier ions move slower than lighter ones. The detector then measures how long each ion takes to travel, revealing both the mass and abundance of different isotopes.
Key insight The biggest peak in mass spectrometry data is called the base peak, whilst the last peak represents the complete molecule (molecular ion peak).
Electrons don't just float randomly around atoms - they follow specific rules. Quantum theory tells us that electrons exist in discrete energy levels called shells, numbered 1, 2, 3, and so on. Think of it like a ladder where electrons can only stand on the rungs, never between them.
These shells are further divided into orbitals (s, p, d, f), each with different shapes and energy levels. The filling order follows a specific pattern 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. Notice how 4s fills before 3d - this catches many students out!
Ionisation energy measures how much energy you need to remove electrons from atoms. Successive ionisation energies increase dramatically when you start removing electrons from inner shells, creating clear jumps in the data that reveal an atom's electronic structure.
Remember Transition metals always lose their 4s electrons first, even though 4s fills before 3d during electron configuration.
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
Explore the principles of mass spectrometry, including relative isotopic mass, relative atomic mass, and the process of molecular fragmentation. This summary covers key concepts such as the calculation of average atomic mass, the role of isotopes, and the interpretation of mass spectra. Ideal for students studying chemical analysis and isotopic abundance.
ChemistryExplore the principles of mass spectrometry, including molecular fragmentation, mass spectra interpretation, and relative abundance analysis. This summary provides essential insights for AQA A-Level organic chemistry, helping students understand how to deduce molecular structures and identify compounds through mass spectrometry techniques.
ChemistryExplore essential calculations and concepts related to moles in chemistry. This summary covers molar mass, concentration, ideal gas equations, empirical and molecular formulas, and the significance of atom economy in chemical processes. Ideal for A-Level Chemistry students seeking to master the topic of 'Amount of Substance'.
ChemistryExplore the principles of mass spectrometry, including the calculation of relative atomic mass and the significance of isotopes. This summary covers key concepts such as isotopic mass, relative abundance, and the impact of vacuum conditions on ion behavior. Ideal for chemistry students preparing for exams.
ChemistryDive into A-Level Chemistry with this comprehensive guide on mole calculations, including mole conversions, molar mass, and stoichiometry. This resource covers essential equations, practical examples, and detailed explanations to help you master the concepts of moles and their applications in gas volume and relative formula mass. Perfect for exam preparation and enhancing your understanding of quantitative chemistry.
ChemistryDive into the essentials of mole calculations, including empirical and molecular formulas, molar mass, and relative formula mass. This summary provides clear explanations and examples to help you master the concepts of chemical formulas and their calculations. Ideal for students preparing for exams or needing a quick reference.
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
Imogen
@iimogen.
Atomic structure might seem complex, but it's actually the foundation that explains how everything around you works. From calculating atomic masses to understanding why electrons behave the way they do, these concepts will help you make sense of chemistry at... Show more
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Ever wondered how scientists figure out the exact mass of atoms? Relative Atomic Mass (RAM) compares an atom's mass to 1/12 of a carbon-12 atom's mass. When you're dealing with isotopes (atoms with different numbers of neutrons), you calculate RAM using a weighted average.
Here's a quick example: if copper has 50.1% Cu-63 and 49.9% Cu-65, you'd calculate: (50.1×63 + 49.9×65) ÷ 100 = 63.50. The percentages act as weights because they show how common each isotope is in nature.
Mass spectrometry is the tool that makes these measurements possible. It works by accelerating ionised samples through a flight path - heavier ions move slower than lighter ones. The detector then measures how long each ion takes to travel, revealing both the mass and abundance of different isotopes.
Key insight: The biggest peak in mass spectrometry data is called the base peak, whilst the last peak represents the complete molecule (molecular ion peak).
Electrons don't just float randomly around atoms - they follow specific rules. Quantum theory tells us that electrons exist in discrete energy levels called shells, numbered 1, 2, 3, and so on. Think of it like a ladder where electrons can only stand on the rungs, never between them.
These shells are further divided into orbitals (s, p, d, f), each with different shapes and energy levels. The filling order follows a specific pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. Notice how 4s fills before 3d - this catches many students out!
Ionisation energy measures how much energy you need to remove electrons from atoms. Successive ionisation energies increase dramatically when you start removing electrons from inner shells, creating clear jumps in the data that reveal an atom's electronic structure.
Remember: Transition metals always lose their 4s electrons first, even though 4s fills before 3d during electron configuration.
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.
4
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the principles of mass spectrometry, including relative isotopic mass, relative atomic mass, and the process of molecular fragmentation. This summary covers key concepts such as the calculation of average atomic mass, the role of isotopes, and the interpretation of mass spectra. Ideal for students studying chemical analysis and isotopic abundance.
ChemistryExplore the principles of mass spectrometry, including molecular fragmentation, mass spectra interpretation, and relative abundance analysis. This summary provides essential insights for AQA A-Level organic chemistry, helping students understand how to deduce molecular structures and identify compounds through mass spectrometry techniques.
ChemistryExplore essential calculations and concepts related to moles in chemistry. This summary covers molar mass, concentration, ideal gas equations, empirical and molecular formulas, and the significance of atom economy in chemical processes. Ideal for A-Level Chemistry students seeking to master the topic of 'Amount of Substance'.
ChemistryExplore the principles of mass spectrometry, including the calculation of relative atomic mass and the significance of isotopes. This summary covers key concepts such as isotopic mass, relative abundance, and the impact of vacuum conditions on ion behavior. Ideal for chemistry students preparing for exams.
ChemistryDive into A-Level Chemistry with this comprehensive guide on mole calculations, including mole conversions, molar mass, and stoichiometry. This resource covers essential equations, practical examples, and detailed explanations to help you master the concepts of moles and their applications in gas volume and relative formula mass. Perfect for exam preparation and enhancing your understanding of quantitative chemistry.
ChemistryDive into the essentials of mole calculations, including empirical and molecular formulas, molar mass, and relative formula mass. This summary provides clear explanations and examples to help you master the concepts of chemical formulas and their calculations. Ideal for students preparing for exams or needing a quick reference.
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