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
6 Dec 2025
192
6 pages
Ummi @ummi_.com
Ever wondered why salt dissolves in water but shatters when you hit it with a hammer? It's all... Show more
Think of ionic bonding as the ultimate example of opposites attracting! Ionic bonding forms when electrons jump from metal atoms to non-metal atoms, creating charged particles that stick together like magnets.
Here's how it works metals lose electrons to become positively charged cations, whilst non-metals gain electrons to become negatively charged anions. Once you've got these opposite charges, electrostatic attraction pulls them together to form the ionic bond.
The driving force behind all this is atoms trying to achieve the octet rule - having eight electrons in their outer shell for maximum stability. It's like atoms have a comfort zone they're desperately trying to reach!
Key Point Remember that metals are the electron donors (they lose electrons), whilst non-metals are the electron acceptors (they gain electrons).
Ionic compounds have some pretty distinctive characteristics that make them easy to spot. They've got high melting and boiling points because those electrostatic forces are incredibly strong - you need loads of energy to break them apart.
You'll always find these compounds arranged in crystalline structures, where ions line up in neat, repeating patterns called crystal lattices. Many are soluble in water because water molecules love to surround and separate the ions.
Here's something cool whilst solid ionic compounds don't conduct electricity, they become excellent conductors when dissolved or melted because the ions can move freely. However, they're also brittle - one small shift in the structure and the whole thing can shatter.
Key Point The combination of high melting points, crystalline structure, and brittleness makes ionic compounds perfect for applications like ceramics and building materials.
Let's look at some ionic compounds you encounter every day. Sodium chloride (NaCl) - your everyday table salt - forms when sodium loses one electron (Na⁺) and chlorine gains one (Cl⁻).
Magnesium oxide (MgO) is trickier because magnesium loses two electrons (Mg²⁺) whilst oxygen gains two (O²⁻). The charges balance perfectly, creating a super-strong compound used in fireproof materials.
Calcium fluoride (CaF₂) shows how charge balancing works when numbers don't match up. One calcium ion (Ca²⁺) needs two fluoride ions (F⁻) to balance the charges - it's like a chemical equation that must add up to zero.
Key Point Always check that the positive and negative charges balance out in ionic compounds - nature loves electrical neutrality!
Several factors determine whether atoms will form ionic bonds. Electronegativity difference is crucial - you need a big gap between how strongly each atom attracts electrons for ionic bonding to occur.
Ionisation energy matters too - this is how much energy it takes to remove an electron from a metal atom. Lower ionisation energy makes it easier for metals to lose electrons and become cations.
Electron affinity is the flip side - how much an atom wants to gain electrons. Non-metals with high electron affinity are brilliant at forming anions because they really want those extra electrons.
Key Point Think of ionic bonding as a perfect match between an atom that desperately wants to lose electrons and another that's dying to gain them!
Ionic compounds are everywhere in your daily life! Obviously there's table salt (NaCl), but you'll also find Epsom salts (MgSO₄) in bath products and magnesium oxide in antacids.
Many minerals are ionic compounds - calcite (CaCO₃) makes up limestone and marble, whilst these compounds are essential in battery technology as electrolytes that allow ions to flow and generate electricity.
In medicine, sodium bicarbonate (NaHCO₃) works as an antacid, and potassium chloride (KCl) is used in medical treatments. The ability of these compounds to dissolve and conduct electricity makes them perfect for biological applications.
Key Point From the salt on your chips to the minerals in rocks and the electrolytes in sports drinks, ionic compounds are fundamental to both technology and biology.
Real ionic compounds aren't as perfectly ionic as textbooks suggest. Even in highly ionic materials, there's usually some covalent character - meaning electrons aren't completely transferred but shared to some degree.
Polarisability is another complication - ions can get distorted by nearby charges, causing deviations from ideal ionic behaviour. This is especially true for larger ions or when dealing with transition metals.
Understanding these limitations helps explain why some compounds behave differently than predicted and why chemistry can be more complex than simple models suggest.
Key Point Remember that chemical bonding models are useful simplifications - real compounds often show characteristics of multiple bonding types!
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
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Ummi
@ummi_.com
Ever wondered why salt dissolves in water but shatters when you hit it with a hammer? It's all down to ionic bonding - one of the most important ways atoms stick together to form compounds. This type of chemical bonding... Show more
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Think of ionic bonding as the ultimate example of opposites attracting! Ionic bonding forms when electrons jump from metal atoms to non-metal atoms, creating charged particles that stick together like magnets.
Here's how it works: metals lose electrons to become positively charged cations, whilst non-metals gain electrons to become negatively charged anions. Once you've got these opposite charges, electrostatic attraction pulls them together to form the ionic bond.
The driving force behind all this is atoms trying to achieve the octet rule - having eight electrons in their outer shell for maximum stability. It's like atoms have a comfort zone they're desperately trying to reach!
Key Point: Remember that metals are the electron donors (they lose electrons), whilst non-metals are the electron acceptors (they gain electrons).
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ionic compounds have some pretty distinctive characteristics that make them easy to spot. They've got high melting and boiling points because those electrostatic forces are incredibly strong - you need loads of energy to break them apart.
You'll always find these compounds arranged in crystalline structures, where ions line up in neat, repeating patterns called crystal lattices. Many are soluble in water because water molecules love to surround and separate the ions.
Here's something cool: whilst solid ionic compounds don't conduct electricity, they become excellent conductors when dissolved or melted because the ions can move freely. However, they're also brittle - one small shift in the structure and the whole thing can shatter.
Key Point: The combination of high melting points, crystalline structure, and brittleness makes ionic compounds perfect for applications like ceramics and building materials.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Let's look at some ionic compounds you encounter every day. Sodium chloride (NaCl) - your everyday table salt - forms when sodium loses one electron (Na⁺) and chlorine gains one (Cl⁻).
Magnesium oxide (MgO) is trickier because magnesium loses two electrons (Mg²⁺) whilst oxygen gains two (O²⁻). The charges balance perfectly, creating a super-strong compound used in fireproof materials.
Calcium fluoride (CaF₂) shows how charge balancing works when numbers don't match up. One calcium ion (Ca²⁺) needs two fluoride ions (F⁻) to balance the charges - it's like a chemical equation that must add up to zero.
Key Point: Always check that the positive and negative charges balance out in ionic compounds - nature loves electrical neutrality!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Several factors determine whether atoms will form ionic bonds. Electronegativity difference is crucial - you need a big gap between how strongly each atom attracts electrons for ionic bonding to occur.
Ionisation energy matters too - this is how much energy it takes to remove an electron from a metal atom. Lower ionisation energy makes it easier for metals to lose electrons and become cations.
Electron affinity is the flip side - how much an atom wants to gain electrons. Non-metals with high electron affinity are brilliant at forming anions because they really want those extra electrons.
Key Point: Think of ionic bonding as a perfect match between an atom that desperately wants to lose electrons and another that's dying to gain them!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ionic compounds are everywhere in your daily life! Obviously there's table salt (NaCl), but you'll also find Epsom salts (MgSO₄) in bath products and magnesium oxide in antacids.
Many minerals are ionic compounds - calcite (CaCO₃) makes up limestone and marble, whilst these compounds are essential in battery technology as electrolytes that allow ions to flow and generate electricity.
In medicine, sodium bicarbonate (NaHCO₃) works as an antacid, and potassium chloride (KCl) is used in medical treatments. The ability of these compounds to dissolve and conduct electricity makes them perfect for biological applications.
Key Point: From the salt on your chips to the minerals in rocks and the electrolytes in sports drinks, ionic compounds are fundamental to both technology and biology.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Real ionic compounds aren't as perfectly ionic as textbooks suggest. Even in highly ionic materials, there's usually some covalent character - meaning electrons aren't completely transferred but shared to some degree.
Polarisability is another complication - ions can get distorted by nearby charges, causing deviations from ideal ionic behaviour. This is especially true for larger ions or when dealing with transition metals.
Understanding these limitations helps explain why some compounds behave differently than predicted and why chemistry can be more complex than simple models suggest.
Key Point: Remember that chemical bonding models are useful simplifications - real compounds often show characteristics of multiple bonding types!
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.
3
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
App 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