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
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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
77
2 pages
Gavenpreet @gavenpreet_erow
Atoms and molecules are the building blocks of everything around us. These tiny particles form elements, compounds, and... Show more
Atoms are the tiniest particles that cannot be broken down further. They never join with other atoms of the same type and are found in elements like Hydrogen (H). Each element contains only its own type of atoms.
When atoms of the same element join together, they create a molecule. For example, oxygen exists as O₂, meaning two oxygen atoms have joined together. Helium, however, remains as single atoms and doesn't form molecules.
A compound forms when atoms of different elements join together through chemical bonds. Water (H₂O) is a compound made of one oxygen atom bonded with two hydrogen atoms.
Remember this! Everything can be classified as either an element (single type of atom), a compound (different atoms chemically bonded), or a mixture (different elements or compounds mixed together but not chemically bonded).
Atoms may be tiny, but they have their own structure! Each atom has a central nucleus surrounded by even smaller particles called electrons. The nucleus contains protons (positive charge) and neutrons (neutral charge), while electrons (negative charge) orbit around it.
The atomic number tells you how many protons an atom has. Since atoms are normally neutral, the number of electrons equals the number of protons. For example, oxygen has 8 protons, so it also has 8 electrons.
The atomic mass is the total number of protons and neutrons in an atom. For oxygen, the atomic number is 8 (protons), and the atomic mass is 16 .
Quick tip On the periodic table, you'll see the atomic number as a smaller number and the atomic mass as a larger number. For example, sodium (Na) has an atomic number of 11 and an atomic mass of approximately 23.
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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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 fundamental concepts of atoms, ions, isotopes, and their properties. This summary covers atomic structure, the formation of ions, the distinction between elements, compounds, and mixtures, and the historical development of atomic theory. Ideal for GCSE Chemistry students.
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
Gavenpreet
@gavenpreet_erow
Atoms and molecules are the building blocks of everything around us. These tiny particles form elements, compounds, and mixtures that make up our world. Understanding their structure helps us learn how different substances behave and interact.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Atoms are the tiniest particles that cannot be broken down further. They never join with other atoms of the same type and are found in elements like Hydrogen (H). Each element contains only its own type of atoms.
When atoms of the same element join together, they create a molecule. For example, oxygen exists as O₂, meaning two oxygen atoms have joined together. Helium, however, remains as single atoms and doesn't form molecules.
A compound forms when atoms of different elements join together through chemical bonds. Water (H₂O) is a compound made of one oxygen atom bonded with two hydrogen atoms.
Remember this! Everything can be classified as either an element (single type of atom), a compound (different atoms chemically bonded), or a mixture (different elements or compounds mixed together but not chemically bonded).
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Atoms may be tiny, but they have their own structure! Each atom has a central nucleus surrounded by even smaller particles called electrons. The nucleus contains protons (positive charge) and neutrons (neutral charge), while electrons (negative charge) orbit around it.
The atomic number tells you how many protons an atom has. Since atoms are normally neutral, the number of electrons equals the number of protons. For example, oxygen has 8 protons, so it also has 8 electrons.
The atomic mass is the total number of protons and neutrons in an atom. For oxygen, the atomic number is 8 (protons), and the atomic mass is 16 .
Quick tip: On the periodic table, you'll see the atomic number as a smaller number and the atomic mass as a larger number. For example, sodium (Na) has an atomic number of 11 and an atomic mass of approximately 23.
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.
6
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 fundamental concepts of atoms, ions, isotopes, and their properties. This summary covers atomic structure, the formation of ions, the distinction between elements, compounds, and mixtures, and the historical development of atomic theory. Ideal for GCSE Chemistry students.
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