Subjects
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
13 Dec 2025
60
4 pages
_jdce @_jdce
Ever wondered what makes up everything around you? From the air you breathe to your mobile phone, it... Show more
Understanding chemistry starts with knowing the key players in this microscopic world. An atom is the smallest piece of any element that can exist - think of it as nature's Lego brick. Elements are pure substances made from just one type of atom, whilst compounds contain different types of atoms chemically stuck together.
Mixtures are different - they're just atoms mixed together without any chemical bonding, like oil and water. A molecule is simply a group of atoms held together by chemical bonds. Here's a clever trick all compounds are molecules, but not all molecules are compounds!
Inside every atom, you'll find three main particles. Protons and neutrons huddle together in the centre (called the nucleus), whilst electrons zip around in energy levels or shells. Protons have a positive charge, electrons are negative, and neutrons are neutral.
Remember Atoms are mostly empty space - if an atom were the size of a football stadium, the nucleus would be like a marble in the centre!
Reading atomic notation is like cracking a secret code, but it's actually quite straightforward. The big number (mass number) tells you the total protons plus neutrons, whilst the small number (atomic number) shows just the protons. Since atoms are normally neutral, the number of protons always equals the number of electrons.
Isotopes are atoms of the same element with different numbers of neutrons - like identical twins with different weights! They have the same number of protons but varying neutrons, which changes their mass.
Calculating relative atomic mass (RAM) involves averaging out all the isotopes of an element. You multiply each isotope's mass by its percentage abundance, add them together, then divide by 100. It's like working out the average weight of all students in your year group.
Top Tip The atomic number never changes for an element - it's like the element's fingerprint!
Ions are atoms that have gained or lost electrons, giving them an electric charge. When atoms lose electrons, they become positively charged because they now have more protons than electrons. Gain electrons, and they become negatively charged.
Different groups on the periodic table form predictable charges. Group 1 elements lose one electron to become 1+ ions, whilst Group 7 elements gain one electron to become 1- ions. Group 8 elements are already happy with full outer shells, so they don't usually form ions at all.
Think of sodium losing an electron to become Na+, or chlorine gaining one to become Cl-. These charged particles are desperate to pair up with opposite charges, which is how compounds like sodium chloride (table salt) form.
Quick Check Remember that metals typically lose electrons (positive ions) whilst non-metals gain electrons (negative ions)!
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.
1
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of atomic structure, including subatomic particles, electron configurations, and the organization of the periodic table. This summary covers key concepts such as atomic bonding, states of matter, and the distinction between elements, compounds, and mixtures. Ideal for students studying Chemistry and Biology.
BiologyExplore the fundamental concepts of elements, isotopes, and relative atomic mass in this detailed summary. Learn how isotopes differ, the significance of atomic mass units (amu), and how to calculate the relative atomic mass using real examples like chlorine. Ideal for chemistry students seeking clarity on these essential topics.
ChemistryExplore the fundamentals of atomic structure, including subatomic particles, atomic mass, and the distinction between elements, compounds, and mixtures. This summary covers key concepts such as protons, neutrons, electrons, and how they form molecules and compounds. Ideal for students studying chemistry.
ChemistryExplore the fundamental concepts of atomic structure and ion formation in this GCSE chemistry summary. Learn about protons, neutrons, electrons, and how atoms become ions through the loss or gain of electrons. Ideal for students seeking clarity on cations and the balance of charges within atoms.
ChemistryExplore the fundamentals of atomic structure and bonding, including atomic numbers, mass numbers, ionic and covalent bonds, and the periodic table. This summary covers key concepts essential for understanding chemical properties and compound formation. Ideal for chemistry students preparing for exams.
ChemistryExplore the fundamentals of atomic structure, including subatomic particles, elements, and compounds. Learn techniques for separating mixtures such as filtration, crystallization, and distillation. This summary covers key concepts in atomic theory and the development of the atomic model, ideal for students preparing for exams.
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
_jdce
@_jdce
Ever wondered what makes up everything around you? From the air you breathe to your mobile phone, it all comes down to tiny building blocks called atoms. Let's dive into the fascinating world of chemistry and discover how these invisible... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Understanding chemistry starts with knowing the key players in this microscopic world. An atom is the smallest piece of any element that can exist - think of it as nature's Lego brick. Elements are pure substances made from just one type of atom, whilst compounds contain different types of atoms chemically stuck together.
Mixtures are different - they're just atoms mixed together without any chemical bonding, like oil and water. A molecule is simply a group of atoms held together by chemical bonds. Here's a clever trick: all compounds are molecules, but not all molecules are compounds!
Inside every atom, you'll find three main particles. Protons and neutrons huddle together in the centre (called the nucleus), whilst electrons zip around in energy levels or shells. Protons have a positive charge, electrons are negative, and neutrons are neutral.
Remember: Atoms are mostly empty space - if an atom were the size of a football stadium, the nucleus would be like a marble in the centre!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Reading atomic notation is like cracking a secret code, but it's actually quite straightforward. The big number (mass number) tells you the total protons plus neutrons, whilst the small number (atomic number) shows just the protons. Since atoms are normally neutral, the number of protons always equals the number of electrons.
Isotopes are atoms of the same element with different numbers of neutrons - like identical twins with different weights! They have the same number of protons but varying neutrons, which changes their mass.
Calculating relative atomic mass (RAM) involves averaging out all the isotopes of an element. You multiply each isotope's mass by its percentage abundance, add them together, then divide by 100. It's like working out the average weight of all students in your year group.
Top Tip: The atomic number never changes for an element - it's like the element's fingerprint!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ions are atoms that have gained or lost electrons, giving them an electric charge. When atoms lose electrons, they become positively charged because they now have more protons than electrons. Gain electrons, and they become negatively charged.
Different groups on the periodic table form predictable charges. Group 1 elements lose one electron to become 1+ ions, whilst Group 7 elements gain one electron to become 1- ions. Group 8 elements are already happy with full outer shells, so they don't usually form ions at all.
Think of sodium losing an electron to become Na+, or chlorine gaining one to become Cl-. These charged particles are desperate to pair up with opposite charges, which is how compounds like sodium chloride (table salt) form.
Quick Check: Remember that metals typically lose electrons (positive ions) whilst non-metals gain electrons (negative ions)!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
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.
1
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of atomic structure, including subatomic particles, electron configurations, and the organization of the periodic table. This summary covers key concepts such as atomic bonding, states of matter, and the distinction between elements, compounds, and mixtures. Ideal for students studying Chemistry and Biology.
BiologyExplore the fundamental concepts of elements, isotopes, and relative atomic mass in this detailed summary. Learn how isotopes differ, the significance of atomic mass units (amu), and how to calculate the relative atomic mass using real examples like chlorine. Ideal for chemistry students seeking clarity on these essential topics.
ChemistryExplore the fundamentals of atomic structure, including subatomic particles, atomic mass, and the distinction between elements, compounds, and mixtures. This summary covers key concepts such as protons, neutrons, electrons, and how they form molecules and compounds. Ideal for students studying chemistry.
ChemistryExplore the fundamental concepts of atomic structure and ion formation in this GCSE chemistry summary. Learn about protons, neutrons, electrons, and how atoms become ions through the loss or gain of electrons. Ideal for students seeking clarity on cations and the balance of charges within atoms.
ChemistryExplore the fundamentals of atomic structure and bonding, including atomic numbers, mass numbers, ionic and covalent bonds, and the periodic table. This summary covers key concepts essential for understanding chemical properties and compound formation. Ideal for chemistry students preparing for exams.
ChemistryExplore the fundamentals of atomic structure, including subatomic particles, elements, and compounds. Learn techniques for separating mixtures such as filtration, crystallization, and distillation. This summary covers key concepts in atomic theory and the development of the atomic model, ideal for students preparing for exams.
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