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Infection and response
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Organisms respond to changes in their internal and external environments (a-level only)
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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
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6
0
Caitlin
12/12/2025
Chemistry
Ocr a level chemistry
422
•
12 Dec 2025
•
Caitlin
@caitlin_05
Understanding intermolecular forces, electron configuration, and acid-base reactions is crucial... Show more
Ever wondered why some substances melt easily whilst others need loads of heat? It's all down to intermolecular forces - the attractions between molecules that you'll need to master for your exams.
Induced dipole-dipole forces are the weakest type and occur in all molecules. Larger molecules like iodine have bigger electron clouds, creating stronger forces and higher boiling points. That's why straight-chain hydrocarbons have higher boiling points than branched ones - they can pack together more tightly.
Permanent dipole-dipole forces happen between polar molecules like HCl. These are stronger than induced forces because the molecules have permanent positive and negative ends. You can actually test for polar molecules by seeing if a liquid stream bends towards a charged rod!
Hydrogen bonding is the strongest intermolecular force and only occurs with nitrogen, oxygen, or fluorine. This explains why water has such unusual properties - hydrogen bonds make ice less dense than liquid water, which is why ice floats.
Quick Test Tip: Remember that when heating liquids, you're breaking intermolecular forces, not covalent bonds within molecules.
The type of bonding completely determines a substance's properties. Molecular substances like iodine and ammonia have low melting points because you're only breaking weak intermolecular forces. They don't conduct electricity and their water solubility depends on polarity.
Giant ionic compounds like sodium chloride behave totally differently. They're solid at room temperature with high melting points because you need massive energy to break strong electrostatic forces between ions. They conduct when liquid because ions can move freely.
Moving on to electron configuration - this might seem tricky, but it's just about filling electron "parking spaces" in order. The s subshell holds 2 electrons, p holds 6, d holds 10, and f holds 14. Remember that electrons prefer to occupy empty orbitals first before pairing up.
For ions, simply add or remove electrons from the highest energy level. Calcium (Ca) has 20 electrons, but Ca²⁺ has lost 2 electrons, giving it 18. Use noble gas notation like 4s¹ for potassium to save time in exams.
Memory Trick: Higher shell numbers mean electrons are further from the nucleus and have higher energy levels.
Orbitals aren't just abstract concepts - they're actual 3D regions where electrons hang out around the nucleus. Understanding their shapes helps explain how atoms bond and behave.
S orbitals are perfectly spherical, whilst p orbitals are dumbbell-shaped and come in three orientations (px, py, pz). When filling orbitals, electrons spin in opposite directions to minimise repulsion - think of it like they're trying to avoid each other!
The aufbau principle is your roadmap for electron configuration. Fill lower energy levels first, and remember that 4s fills before 3d (even though 3d is written first in the final configuration). For iron (Fe), you get: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s².
When atoms form ions, they lose or gain electrons to achieve stable configurations. This is fundamental to understanding chemical reactivity and bonding patterns you'll encounter throughout A-level chemistry.
Exam Success: Always check your electron numbers add up to the atomic number for neutral atoms!
Acids are proton donors and bases are proton acceptors - this Brønsted-Lowry definition is absolutely essential for A-level success. When acids and bases react, they're essentially swapping protons (H⁺ ions).
Strong acids like HCl, H₂SO₄, and HNO₃ completely dissociate in water, flooding the solution with H⁺ ions. Weak acids like ethanoic acid only partially dissociate, creating an equilibrium. The same principle applies to strong bases (NaOH, KOH) versus weak bases (NH₃).
Neutralisation reactions always follow the same pattern: acid + base → salt + water. The key reaction is H⁺ + OH⁻ → H₂O. You'll also need to know that metals react with acids to produce hydrogen gas, whilst metal carbonates produce carbon dioxide.
Polyprotic acids can donate multiple protons - monoprotic (like HNO₃), diprotic (like H₂SO₄), or triprotic (like H₃PO₄). This affects stoichiometry in calculations, so always check how many protons each acid can donate.
Equation Mastery: Learn the ionic equations - they show what's actually happening chemically and often earn extra marks in exams.
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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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
Caitlin
@caitlin_05
Understanding intermolecular forces, electron configuration, and acid-base reactions is crucial for success in A-level chemistry. These fundamental concepts explain everything from why water forms ice to how atoms bond and react with each other.
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Ever wondered why some substances melt easily whilst others need loads of heat? It's all down to intermolecular forces - the attractions between molecules that you'll need to master for your exams.
Induced dipole-dipole forces are the weakest type and occur in all molecules. Larger molecules like iodine have bigger electron clouds, creating stronger forces and higher boiling points. That's why straight-chain hydrocarbons have higher boiling points than branched ones - they can pack together more tightly.
Permanent dipole-dipole forces happen between polar molecules like HCl. These are stronger than induced forces because the molecules have permanent positive and negative ends. You can actually test for polar molecules by seeing if a liquid stream bends towards a charged rod!
Hydrogen bonding is the strongest intermolecular force and only occurs with nitrogen, oxygen, or fluorine. This explains why water has such unusual properties - hydrogen bonds make ice less dense than liquid water, which is why ice floats.
Quick Test Tip: Remember that when heating liquids, you're breaking intermolecular forces, not covalent bonds within molecules.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The type of bonding completely determines a substance's properties. Molecular substances like iodine and ammonia have low melting points because you're only breaking weak intermolecular forces. They don't conduct electricity and their water solubility depends on polarity.
Giant ionic compounds like sodium chloride behave totally differently. They're solid at room temperature with high melting points because you need massive energy to break strong electrostatic forces between ions. They conduct when liquid because ions can move freely.
Moving on to electron configuration - this might seem tricky, but it's just about filling electron "parking spaces" in order. The s subshell holds 2 electrons, p holds 6, d holds 10, and f holds 14. Remember that electrons prefer to occupy empty orbitals first before pairing up.
For ions, simply add or remove electrons from the highest energy level. Calcium (Ca) has 20 electrons, but Ca²⁺ has lost 2 electrons, giving it 18. Use noble gas notation like 4s¹ for potassium to save time in exams.
Memory Trick: Higher shell numbers mean electrons are further from the nucleus and have higher energy levels.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Orbitals aren't just abstract concepts - they're actual 3D regions where electrons hang out around the nucleus. Understanding their shapes helps explain how atoms bond and behave.
S orbitals are perfectly spherical, whilst p orbitals are dumbbell-shaped and come in three orientations (px, py, pz). When filling orbitals, electrons spin in opposite directions to minimise repulsion - think of it like they're trying to avoid each other!
The aufbau principle is your roadmap for electron configuration. Fill lower energy levels first, and remember that 4s fills before 3d (even though 3d is written first in the final configuration). For iron (Fe), you get: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s².
When atoms form ions, they lose or gain electrons to achieve stable configurations. This is fundamental to understanding chemical reactivity and bonding patterns you'll encounter throughout A-level chemistry.
Exam Success: Always check your electron numbers add up to the atomic number for neutral atoms!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Acids are proton donors and bases are proton acceptors - this Brønsted-Lowry definition is absolutely essential for A-level success. When acids and bases react, they're essentially swapping protons (H⁺ ions).
Strong acids like HCl, H₂SO₄, and HNO₃ completely dissociate in water, flooding the solution with H⁺ ions. Weak acids like ethanoic acid only partially dissociate, creating an equilibrium. The same principle applies to strong bases (NaOH, KOH) versus weak bases (NH₃).
Neutralisation reactions always follow the same pattern: acid + base → salt + water. The key reaction is H⁺ + OH⁻ → H₂O. You'll also need to know that metals react with acids to produce hydrogen gas, whilst metal carbonates produce carbon dioxide.
Polyprotic acids can donate multiple protons - monoprotic (like HNO₃), diprotic (like H₂SO₄), or triprotic (like H₃PO₄). This affects stoichiometry in calculations, so always check how many protons each acid can donate.
Equation Mastery: Learn the ionic equations - they show what's actually happening chemically and often earn extra marks in exams.
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 intricacies of chemical bonding, including covalent and ionic interactions, molecular shapes, and bond angles. This summary covers key concepts such as tetrahedral and octahedral geometries, lone pairs, and the effects of molecular structure on properties. Ideal for A-level chemistry students seeking to understand the fundamentals of molecular geometry and bonding forces.
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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