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23 Dec 2025
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Understanding Homologous Series in Chemistry
Charlotte
@charlotte638394
1 / 6
Homologous Series
You're about to master one of chemistry's most useful concepts that explains everything from the fuel in cars to the materials in your phone case. Homologous series are like chemical families where all members share the same DNA - they follow the same rules and behave in similar ways.
Think of it as chemistry's version of a recipe book. Once you understand the pattern, you can predict how thousands of different compounds will behave just by looking at their structure.
Quick Tip: Homologous series are the key to understanding organic chemistry - master this concept and you've cracked the code for most carbon-based molecules!
Hydrocarbons
Hydrocarbons are the simplest carbon compounds you'll encounter - they're made of just hydrogen and carbon atoms. That's it! Despite this simplicity, they form the backbone of countless materials we use daily.
A homologous series is essentially a family of compounds that all share the same general formula and have similar chemical properties. It's like having a template that you can use to build different molecules by adding more carbon atoms.
Each member of a homologous series behaves predictably, which is why chemists can make accurate predictions about compounds they've never even seen before.
Remember: All hydrocarbons contain only carbon and hydrogen - no other elements allowed in this exclusive club!
Alkanes
Alkanes are the most stable members of the hydrocarbon family. They're called saturated hydrocarbons because every carbon atom is surrounded by as many hydrogen atoms as possible - there's no room for more!
The general formula for alkanes is C₍n₎H₍₂n+₂₎. This mathematical relationship means you can work out the formula for any alkane just by knowing how many carbon atoms it contains. Pretty neat, right?
Alkanes only contain single covalent bonds, which makes them quite unreactive compared to other hydrocarbons. They're also insoluble in water, which explains why oil floats on water rather than mixing with it.
Exam Tip: Remember that "saturated" means single bonds only - no double or triple bonds allowed in alkanes!
Alkenes
Alkenes are the rebels of the hydrocarbon world. Unlike their stable alkane cousins, alkenes are unsaturated hydrocarbons that contain at least one carbon-to-carbon double bond. This double bond is what makes them much more reactive and interesting!
The general formula for alkenes is C₍n₎H₍₂n₎. Notice how they have fewer hydrogen atoms than alkanes - that's because of the double bond taking up space.
Here's a brilliant test you can use: unsaturated hydrocarbons quickly decolourise bromine water. This colour change happens fast and is a dead giveaway that you're dealing with an alkene rather than an alkane.
Lab Trick: The bromine water test is your go-to method for spotting alkenes - orange to colourless in seconds!
Cycloalkanes
Cycloalkanes are the tricksters of organic chemistry. They have the same general formula as alkenes (C₍n₎H₍₂n₎), but don't let that fool you - they behave completely differently!
Even though cycloalkanes share the same formula as alkenes, they're actually saturated hydrocarbons that contain only single bonds. The "missing" hydrogen atoms aren't really missing - they're just not needed because the carbon atoms form a ring structure.
Because cycloalkanes only have single bonds, they don't quickly decolourise bromine solution like alkenes do. This is a crucial difference that often trips up students in exams!
Key Point: Same formula as alkenes, but completely different behaviour - cycloalkanes are saturated despite having fewer hydrogen atoms!
Isomers
Isomers are like identical twins with different personalities. They have exactly the same molecular formula (same number of each type of atom) but completely different structural formulas (atoms arranged differently).
This different arrangement means isomers can have surprisingly different physical and chemical properties. One might be a gas whilst its isomer is a liquid, or one might be toxic whilst the other is harmless!
Understanding isomers explains why there are so many different compounds possible with just a few elements - it's all about how you arrange the atoms, not just what atoms you have.
Mind-Blower: Some isomers are so different that one might be used as medicine whilst another with the exact same atoms could be poisonous!
We thought you’d never ask...
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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
Understanding Homologous Series in Chemistry
Charlotte
@charlotte638394
Ever wondered why petrol, cooking gas, and plastic bags are all so different despite being made from the same basic ingredients? It's all about homologous series- families of carbon compounds that follow predictable patterns and make up most of... Show more
Homologous Series
You're about to master one of chemistry's most useful concepts that explains everything from the fuel in cars to the materials in your phone case. Homologous series are like chemical families where all members share the same DNA - they follow the same rules and behave in similar ways.
Think of it as chemistry's version of a recipe book. Once you understand the pattern, you can predict how thousands of different compounds will behave just by looking at their structure.
Quick Tip: Homologous series are the key to understanding organic chemistry - master this concept and you've cracked the code for most carbon-based molecules!
Sign up to see the contentIt's free!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Hydrocarbons
Hydrocarbons are the simplest carbon compounds you'll encounter - they're made of just hydrogen and carbon atoms. That's it! Despite this simplicity, they form the backbone of countless materials we use daily.
A homologous series is essentially a family of compounds that all share the same general formula and have similar chemical properties. It's like having a template that you can use to build different molecules by adding more carbon atoms.
Each member of a homologous series behaves predictably, which is why chemists can make accurate predictions about compounds they've never even seen before.
Remember: All hydrocarbons contain only carbon and hydrogen - no other elements allowed in this exclusive club!
Sign up to see the contentIt's free!
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Alkanes
Alkanes are the most stable members of the hydrocarbon family. They're called saturated hydrocarbons because every carbon atom is surrounded by as many hydrogen atoms as possible - there's no room for more!
The general formula for alkanes is C₍n₎H₍₂n+₂₎. This mathematical relationship means you can work out the formula for any alkane just by knowing how many carbon atoms it contains. Pretty neat, right?
Alkanes only contain single covalent bonds, which makes them quite unreactive compared to other hydrocarbons. They're also insoluble in water, which explains why oil floats on water rather than mixing with it.
Exam Tip: Remember that "saturated" means single bonds only - no double or triple bonds allowed in alkanes!
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By signing up you accept Terms of Service and Privacy Policy
Alkenes
Alkenes are the rebels of the hydrocarbon world. Unlike their stable alkane cousins, alkenes are unsaturated hydrocarbons that contain at least one carbon-to-carbon double bond. This double bond is what makes them much more reactive and interesting!
The general formula for alkenes is C₍n₎H₍₂n₎. Notice how they have fewer hydrogen atoms than alkanes - that's because of the double bond taking up space.
Here's a brilliant test you can use: unsaturated hydrocarbons quickly decolourise bromine water. This colour change happens fast and is a dead giveaway that you're dealing with an alkene rather than an alkane.
Lab Trick: The bromine water test is your go-to method for spotting alkenes - orange to colourless in seconds!
Sign up to see the contentIt's free!
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Cycloalkanes
Cycloalkanes are the tricksters of organic chemistry. They have the same general formula as alkenes (C₍n₎H₍₂n₎), but don't let that fool you - they behave completely differently!
Even though cycloalkanes share the same formula as alkenes, they're actually saturated hydrocarbons that contain only single bonds. The "missing" hydrogen atoms aren't really missing - they're just not needed because the carbon atoms form a ring structure.
Because cycloalkanes only have single bonds, they don't quickly decolourise bromine solution like alkenes do. This is a crucial difference that often trips up students in exams!
Key Point: Same formula as alkenes, but completely different behaviour - cycloalkanes are saturated despite having fewer hydrogen atoms!
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Isomers
Isomers are like identical twins with different personalities. They have exactly the same molecular formula (same number of each type of atom) but completely different structural formulas (atoms arranged differently).
This different arrangement means isomers can have surprisingly different physical and chemical properties. One might be a gas whilst its isomer is a liquid, or one might be toxic whilst the other is harmless!
Understanding isomers explains why there are so many different compounds possible with just a few elements - it's all about how you arrange the atoms, not just what atoms you have.
Mind-Blower: Some isomers are so different that one might be used as medicine whilst another with the exact same atoms could be poisonous!
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?
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Is Knowunity really free of charge?
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Most popular content: Homologous Series
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4.9/5
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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