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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
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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
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2s the making of modern britain, 1951-2007
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Chemistry
2 Dec 2025
169
3 pages
hammerbro @hammerbro
Ever wonder why water boils at 100°C whilst other similar molecules boil at much lower temperatures? It's all... Show more
Think of intermolecular forces as the "glue" that holds molecules together, though they're much weaker than the bonds within molecules themselves. These forces might be weak, but they're absolutely crucial for determining how substances behave in the real world.
There are three main types you need to know Van der Waals forces (the weakest), permanent dipole-dipole interactions (medium strength), and hydrogen bonding (the strongest). Each one works differently and affects substances in unique ways.
Van der Waals forces are the most basic type - they exist between all molecules and even noble gas atoms. As molecules get larger, these forces become stronger because there's more surface area for attraction. This explains why helium boils at -269°C whilst xenon boils at -108°C.
Quick Check Remember that molecular size directly affects Van der Waals forces - bigger molecules = stronger forces = higher boiling points!
Permanent dipole-dipole interactions occur when molecules have uneven charge distribution due to differences in electronegativity. Picture HCl molecules lining up so the slightly positive hydrogen end attracts the slightly negative chlorine end of neighbouring molecules.
Hydrogen bonding takes this concept further and creates the strongest intermolecular force. It only happens when hydrogen is bonded to fluorine, oxygen, or nitrogen - the three most electronegative elements. The hydrogen's positive charge attracts lone pairs of electrons on these atoms.
Water perfectly demonstrates hydrogen bonding in action. These special bonds give water its unique properties ice is less dense than liquid water (creating the lattice structure that makes ice float), water has an unusually high boiling point, and it shows remarkable surface tension.
Real-World Connection Without hydrogen bonding, water would boil at around -80°C, making life on Earth impossible!
Looking at hydrides (compounds of hydrogen with other elements) reveals fascinating patterns. In Groups 5, 6, and 7, the first member always has a much higher boiling point than expected - NH₃, H₂O, and HF all break the trend because of hydrogen bonding.
For other hydrides moving down each group, two competing factors battle it out. Polarity decreases (weakening dipole forces) whilst molecular size increases (strengthening Van der Waals forces). The size effect usually wins, explaining why H₂Te boils higher than H₂S.
Here are the essential rules you need to remember all molecules have Van der Waals forces as a baseline, polar molecules add dipole-dipole forces on top, and hydrogen bonding only occurs with F, O, or N. These forces directly determine physical properties like boiling points, melting points, and solubility.
Exam Tip When predicting boiling points, first check for hydrogen bonding, then consider molecular size and polarity - this approach works every time!
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
Explore the fundamentals of London Dispersion Forces (LDFs), the weakest type of intermolecular forces. This summary covers the formation of temporary dipoles, the role of electron movement, and how these forces affect the properties of non-polar molecules, including their low melting and boiling points. Ideal for students studying higher chemistry concepts.
ChemistryExplore the key types of intermolecular forces including London Dispersion Forces, Permanent Dipole-Permanent Dipole Interactions, and Hydrogen Bonding. This summary provides a clear understanding of their characteristics, strengths, and examples, essential for Higher Chemistry studies.
ChemistryExplore key concepts in redox reactions, including oxidation and reduction processes, half-equations, and the role of oxidizing and reducing agents. Understand periodic trends such as electronegativity, ionization energy, and molecular structure. This summary covers essential topics for higher chemistry, focusing on the periodic table and intermolecular forces.
ChemistryExplore the fundamental concepts of atomic structure, ionic and covalent bonding, and the properties of materials. This summary covers nanoparticles, giant covalent structures, metallic bonding, and the behavior of different compounds, providing essential insights for chemistry students. Ideal for exam preparation and revision.
ChemistryExplore the principles of electrolysis, including redox reactions, half-reactions, and the roles of anodes and cathodes. This summary covers key concepts such as electrolytic cells, Faraday's laws, and the significance of electrolytes in conducting electricity. Ideal for students preparing for exams or seeking a clear understanding of electrolysis processes.
ChemistryComprehensive A Level Chemistry summary covering key concepts of bonding types, molecular shapes, electronegativity, and intermolecular forces. Understand ionic, covalent, and dative bonds, along with their properties and effects on molecular behavior. Ideal for exam preparation and revision.
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
hammerbro
@hammerbro
Ever wonder why water boils at 100°C whilst other similar molecules boil at much lower temperatures? It's all down to intermolecular forces - the invisible attractions between molecules that determine how substances behave. Understanding these forces will help you predict... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Think of intermolecular forces as the "glue" that holds molecules together, though they're much weaker than the bonds within molecules themselves. These forces might be weak, but they're absolutely crucial for determining how substances behave in the real world.
There are three main types you need to know: Van der Waals forces (the weakest), permanent dipole-dipole interactions (medium strength), and hydrogen bonding (the strongest). Each one works differently and affects substances in unique ways.
Van der Waals forces are the most basic type - they exist between all molecules and even noble gas atoms. As molecules get larger, these forces become stronger because there's more surface area for attraction. This explains why helium boils at -269°C whilst xenon boils at -108°C.
Quick Check: Remember that molecular size directly affects Van der Waals forces - bigger molecules = stronger forces = higher boiling points!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Permanent dipole-dipole interactions occur when molecules have uneven charge distribution due to differences in electronegativity. Picture HCl molecules lining up so the slightly positive hydrogen end attracts the slightly negative chlorine end of neighbouring molecules.
Hydrogen bonding takes this concept further and creates the strongest intermolecular force. It only happens when hydrogen is bonded to fluorine, oxygen, or nitrogen - the three most electronegative elements. The hydrogen's positive charge attracts lone pairs of electrons on these atoms.
Water perfectly demonstrates hydrogen bonding in action. These special bonds give water its unique properties: ice is less dense than liquid water (creating the lattice structure that makes ice float), water has an unusually high boiling point, and it shows remarkable surface tension.
Real-World Connection: Without hydrogen bonding, water would boil at around -80°C, making life on Earth impossible!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Looking at hydrides (compounds of hydrogen with other elements) reveals fascinating patterns. In Groups 5, 6, and 7, the first member always has a much higher boiling point than expected - NH₃, H₂O, and HF all break the trend because of hydrogen bonding.
For other hydrides moving down each group, two competing factors battle it out. Polarity decreases (weakening dipole forces) whilst molecular size increases (strengthening Van der Waals forces). The size effect usually wins, explaining why H₂Te boils higher than H₂S.
Here are the essential rules you need to remember: all molecules have Van der Waals forces as a baseline, polar molecules add dipole-dipole forces on top, and hydrogen bonding only occurs with F, O, or N. These forces directly determine physical properties like boiling points, melting points, and solubility.
Exam Tip: When predicting boiling points, first check for hydrogen bonding, then consider molecular size and polarity - this approach works every time!
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.
10
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of London Dispersion Forces (LDFs), the weakest type of intermolecular forces. This summary covers the formation of temporary dipoles, the role of electron movement, and how these forces affect the properties of non-polar molecules, including their low melting and boiling points. Ideal for students studying higher chemistry concepts.
ChemistryExplore the key types of intermolecular forces including London Dispersion Forces, Permanent Dipole-Permanent Dipole Interactions, and Hydrogen Bonding. This summary provides a clear understanding of their characteristics, strengths, and examples, essential for Higher Chemistry studies.
ChemistryExplore key concepts in redox reactions, including oxidation and reduction processes, half-equations, and the role of oxidizing and reducing agents. Understand periodic trends such as electronegativity, ionization energy, and molecular structure. This summary covers essential topics for higher chemistry, focusing on the periodic table and intermolecular forces.
ChemistryExplore the fundamental concepts of atomic structure, ionic and covalent bonding, and the properties of materials. This summary covers nanoparticles, giant covalent structures, metallic bonding, and the behavior of different compounds, providing essential insights for chemistry students. Ideal for exam preparation and revision.
ChemistryExplore the principles of electrolysis, including redox reactions, half-reactions, and the roles of anodes and cathodes. This summary covers key concepts such as electrolytic cells, Faraday's laws, and the significance of electrolytes in conducting electricity. Ideal for students preparing for exams or seeking a clear understanding of electrolysis processes.
ChemistryComprehensive A Level Chemistry summary covering key concepts of bonding types, molecular shapes, electronegativity, and intermolecular forces. Understand ionic, covalent, and dative bonds, along with their properties and effects on molecular behavior. Ideal for exam preparation and revision.
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