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Isha Patel
12/12/2025
Chemistry
Chemistry topic revision
121
•
12 Dec 2025
•
Complete Chemistry Revision Guide
Isha Patel
@ishx_0119
1 / 5
Atomic Structure and the Periodic Table
Every atom is made up of three key particles that you need to know inside out. Protons have a mass of 1 and a positive charge, whilst neutrons also have a mass of 1 but no charge - both live in the nucleus at the atom's centre. Electrons are tiny with a negative charge, and they orbit around the nucleus.
The periodic table is brilliantly organised to help you understand atoms. The atomic number tells you how many protons an atom has, and in neutral atoms, this equals the number of electrons too. Groups (vertical columns) show how many electrons are in the outer shell, whilst periods (horizontal rows) indicate the number of electron shells.
Isotopes are atoms with the same number of protons but different neutrons - they're like identical twins with different weights! Ions are atoms that have gained or lost electrons, giving them a charge.
Quick Tip: The group number directly tells you the charge an ion will have - Group 1 becomes 1+, Group 7 becomes 1-, and so on!
Types of Chemical Bonding
Think of ionic bonding as the ultimate give-and-take relationship between metals and non-metals. Metals desperately want to lose their outer electrons (becoming positive ions), whilst non-metals are keen to gain electrons to fill their outer shell (becoming negative ions). The result? Oppositely charged ions that attract each other through electrostatic forces.
Covalent bonding happens when two non-metals decide to share electrons rather than transfer them. Hydrogen molecules share one pair of electrons (single bond), whilst oxygen molecules share two pairs (double bond). It's teamwork at the atomic level!
Metallic bonding creates a 'sea of delocalised electrons' around positive metal ions. These free-floating electrons can move throughout the structure, which explains why metals conduct electricity so well.
Remember: Ionic = transfer electrons, Covalent = share electrons, Metallic = delocalised electron sea!
Properties of Ionic and Simple Covalent Compounds
Ionic compounds are tough cookies with high melting and boiling points because those electrostatic attractions between ions are seriously strong. They only conduct electricity when molten or dissolved because the ions need to be free to move. However, they're quite brittle - apply force and the layers shift, causing like charges to repel and the structure to shatter.
Simple covalent molecules are completely different beasts. When you heat them, you're not breaking the strong covalent bonds within molecules - you're breaking the much weaker intermolecular forces between separate molecules. This is why substances like ammonia have relatively low boiling points.
These molecules don't conduct electricity because they're neutral overall - no charged particles means no electrical flow. As molecules get larger with more electrons, their intermolecular forces become stronger, making them harder to separate.
Key Point: In ionic compounds, you conduct because ions move; in metals, you conduct because electrons move; in simple molecules, you don't conduct at all!
Giant Covalent Structures
Giant covalent substances are like one massive molecule where atoms are joined by covalent bonds in a continuous network. Unlike simple molecules, there are no separate units - it's all connected! This gives them incredibly high melting and boiling points because you'd need to break countless strong covalent bonds.
Diamond is pure carbon where each atom bonds to four others in a tetrahedral structure, making it extremely hard and strong. It can't conduct electricity because all electrons are locked in bonds.
Graphite is also pure carbon, but arranged in hexagonal layers where each atom bonds to just three others. This leaves delocalised electrons that can conduct electricity, and the layers can slide over each other, making graphite soft and slippery - perfect for pencils!
Graphene (single layer of graphite) and Buckminster fullerene show how the same element can have completely different properties based on structure.
Cool Fact: Graphene is just one atom thick but stronger than steel - it's the thinnest material ever isolated!
Metals and Silicon Dioxide
Silicon dioxide (silica) forms giant covalent structures similar to diamond, with high melting points and no electrical conductivity. You know it as sand! Its tetrahedral structure creates strong covalent bonds throughout, making it incredibly stable.
Metals have brilliant properties that make them incredibly useful. Their high melting and boiling points come from strong metallic bonds, whilst their delocalised electrons make them excellent conductors of both electricity and heat. The electron sea also allows metal layers to slide over each other, making them malleable (bendable) and ductile (drawable into wires).
Most metals are shiny when freshly cut and some are magnetic - but only iron, nickel, and cobalt show strong magnetic properties. These properties explain why metals dominate construction, electronics, and engineering.
Top Tip: Only three elements are strongly magnetic - iron, nickel, and cobalt. Everything else showing magnetism contains one of these!
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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
Complete Chemistry Revision Guide
Isha Patel
@ishx_0119
Understanding atoms and how they bond together is fundamental to chemistry - and it's easier than you might think! This covers everything from atomic structure to the three main types of bonding that create all the materials around you.
Atomic Structure and the Periodic Table
Every atom is made up of three key particles that you need to know inside out. Protons have a mass of 1 and a positive charge, whilst neutrons also have a mass of 1 but no charge - both live in the nucleus at the atom's centre. Electrons are tiny with a negative charge, and they orbit around the nucleus.
The periodic table is brilliantly organised to help you understand atoms. The atomic number tells you how many protons an atom has, and in neutral atoms, this equals the number of electrons too. Groups (vertical columns) show how many electrons are in the outer shell, whilst periods (horizontal rows) indicate the number of electron shells.
Isotopes are atoms with the same number of protons but different neutrons - they're like identical twins with different weights! Ions are atoms that have gained or lost electrons, giving them a charge.
Quick Tip: The group number directly tells you the charge an ion will have - Group 1 becomes 1+, Group 7 becomes 1-, and so on!
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Improve your grades
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Types of Chemical Bonding
Think of ionic bonding as the ultimate give-and-take relationship between metals and non-metals. Metals desperately want to lose their outer electrons (becoming positive ions), whilst non-metals are keen to gain electrons to fill their outer shell (becoming negative ions). The result? Oppositely charged ions that attract each other through electrostatic forces.
Covalent bonding happens when two non-metals decide to share electrons rather than transfer them. Hydrogen molecules share one pair of electrons (single bond), whilst oxygen molecules share two pairs (double bond). It's teamwork at the atomic level!
Metallic bonding creates a 'sea of delocalised electrons' around positive metal ions. These free-floating electrons can move throughout the structure, which explains why metals conduct electricity so well.
Remember: Ionic = transfer electrons, Covalent = share electrons, Metallic = delocalised electron sea!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Properties of Ionic and Simple Covalent Compounds
Ionic compounds are tough cookies with high melting and boiling points because those electrostatic attractions between ions are seriously strong. They only conduct electricity when molten or dissolved because the ions need to be free to move. However, they're quite brittle - apply force and the layers shift, causing like charges to repel and the structure to shatter.
Simple covalent molecules are completely different beasts. When you heat them, you're not breaking the strong covalent bonds within molecules - you're breaking the much weaker intermolecular forces between separate molecules. This is why substances like ammonia have relatively low boiling points.
These molecules don't conduct electricity because they're neutral overall - no charged particles means no electrical flow. As molecules get larger with more electrons, their intermolecular forces become stronger, making them harder to separate.
Key Point: In ionic compounds, you conduct because ions move; in metals, you conduct because electrons move; in simple molecules, you don't conduct at all!
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Giant Covalent Structures
Giant covalent substances are like one massive molecule where atoms are joined by covalent bonds in a continuous network. Unlike simple molecules, there are no separate units - it's all connected! This gives them incredibly high melting and boiling points because you'd need to break countless strong covalent bonds.
Diamond is pure carbon where each atom bonds to four others in a tetrahedral structure, making it extremely hard and strong. It can't conduct electricity because all electrons are locked in bonds.
Graphite is also pure carbon, but arranged in hexagonal layers where each atom bonds to just three others. This leaves delocalised electrons that can conduct electricity, and the layers can slide over each other, making graphite soft and slippery - perfect for pencils!
Graphene (single layer of graphite) and Buckminster fullerene show how the same element can have completely different properties based on structure.
Cool Fact: Graphene is just one atom thick but stronger than steel - it's the thinnest material ever isolated!
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Metals and Silicon Dioxide
Silicon dioxide (silica) forms giant covalent structures similar to diamond, with high melting points and no electrical conductivity. You know it as sand! Its tetrahedral structure creates strong covalent bonds throughout, making it incredibly stable.
Metals have brilliant properties that make them incredibly useful. Their high melting and boiling points come from strong metallic bonds, whilst their delocalised electrons make them excellent conductors of both electricity and heat. The electron sea also allows metal layers to slide over each other, making them malleable (bendable) and ductile (drawable into wires).
Most metals are shiny when freshly cut and some are magnetic - but only iron, nickel, and cobalt show strong magnetic properties. These properties explain why metals dominate construction, electronics, and engineering.
Top Tip: Only three elements are strongly magnetic - iron, nickel, and cobalt. Everything else showing magnetism contains one of these!
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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Most popular content: Ionic Bonding
Most popular content in Chemistry
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
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