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2 Dec 2025
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Key Mind Maps for National 5 Chemistry Unit 3
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Chemical Cells and Metal Reactivity
Ever wondered how batteries actually work? Chemical cells generate electricity by using the difference in reactivity between metals. When you connect two different metals through an electrolyte (a solution containing ions), electrons naturally flow from the more reactive metal to the less reactive one.
Simple cells have both electrodes in the same electrolyte, whilst complex cells keep each electrode in separate electrolyte solutions connected by a salt bridge. The salt bridge completes the circuit by allowing ions to move between the solutions. The further apart the metals are in the electrochemical series, the higher the voltage you'll get.
Metallic bonding explains why metals conduct electricity so well - it's the electrostatic attraction between positive metal ions and a 'sea' of delocalised electrons that can move freely. Metal reactivity depends on how easily atoms lose electrons to form positive ions.
Key Tip: Remember that more reactive metals are found higher in the reactivity series and lose electrons more easily than less reactive metals.
Polymers and Addition Polymerisation
Plastic bottles, carrier bags, and rubber tyres all start life as tiny molecules called monomers. These small building blocks join together in a process called polymerisation to create huge chain-like molecules called polymers.
Addition polymerisation happens when monomers containing double bonds (like alkenes) link together. The double bond breaks open, allowing the molecules to connect in long chains. For example, thousands of ethene molecules join to make poly(ethene) - the plastic used in shopping bags.
The naming system is straightforward: just add 'poly' before the monomer name in brackets. So ethene becomes poly(ethene), and propene becomes poly(propene). Rubber is actually a natural polymer formed through addition polymerisation of plant molecules.
Remember: All addition polymerisation monomers must contain a C=C double bond, and no other products are formed - just the long polymer chain.
Industrial Chemistry and Fertilisers
Plants need three essential elements to grow properly: nitrogen (N), phosphorus (P), and potassium (K) - that's why you'll see NPK on fertiliser packets. Any good fertiliser must contain at least one of these elements and be water-soluble so plant roots can absorb it.
The Haber process manufactures ammonia (NH₃) industrially by combining nitrogen and hydrogen gases. This reversible reaction uses high pressure and an iron catalyst to speed things up. It's economical because unreacted gases get recycled back through the system.
The Ostwald process then converts this ammonia into nitric acid (HNO₃). Ammonia gets oxidised to nitrogen monoxide using a platinum catalyst, then further oxidised to nitrogen dioxide, which dissolves in water to make nitric acid. This acid is crucial for making fertilisers like ammonium nitrate.
Industrial Insight: Both processes use catalysts to speed up reactions without being used up - platinum for the Ostwald process and iron for the Haber process.
Radioactivity and Half-Life
Radioactive decay happens when unstable atomic nuclei break apart, releasing three types of radiation: alpha particles , beta particles (electrons), and gamma rays (electromagnetic waves). Each type has different penetrating power - paper stops alpha, aluminium stops beta, but you need thick concrete or lead to stop gamma rays.
Half-life is the time it takes for exactly half of a radioactive sample to decay. This rate is completely constant - nothing can speed it up or slow it down. If you start with 100g of a substance with a 14-day half-life, you'll have 50g after 14 days, 25g after 28 days, and so on.
Radioactivity has many practical uses in everyday life. Carbon-14 dating helps archaeologists determine the age of ancient organic materials, iodine-123 helps doctors detect thyroid problems, and americium-241 in smoke alarms detects particles from fires.
Safety Note: The penetrating power increases from alpha to gamma, but so does the difficulty in stopping the radiation - that's why different materials are needed for shielding.
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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.
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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.
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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
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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
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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
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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
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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
Key Mind Maps for National 5 Chemistry Unit 3
hannahsrevision
@hannahsrevision
This chemistry unit covers four fundamental topics that connect basic atomic theory to real-world applications. You'll explore how electricity works in chemical cells, how small molecules build into plastics, how we make fertilisers industrially, and how radioactive materials behave and... Show more
Chemical Cells and Metal Reactivity
Ever wondered how batteries actually work? Chemical cells generate electricity by using the difference in reactivity between metals. When you connect two different metals through an electrolyte (a solution containing ions), electrons naturally flow from the more reactive metal to the less reactive one.
Simple cells have both electrodes in the same electrolyte, whilst complex cells keep each electrode in separate electrolyte solutions connected by a salt bridge. The salt bridge completes the circuit by allowing ions to move between the solutions. The further apart the metals are in the electrochemical series, the higher the voltage you'll get.
Metallic bonding explains why metals conduct electricity so well - it's the electrostatic attraction between positive metal ions and a 'sea' of delocalised electrons that can move freely. Metal reactivity depends on how easily atoms lose electrons to form positive ions.
Key Tip: Remember that more reactive metals are found higher in the reactivity series and lose electrons more easily than less reactive metals.
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Polymers and Addition Polymerisation
Plastic bottles, carrier bags, and rubber tyres all start life as tiny molecules called monomers. These small building blocks join together in a process called polymerisation to create huge chain-like molecules called polymers.
Addition polymerisation happens when monomers containing double bonds (like alkenes) link together. The double bond breaks open, allowing the molecules to connect in long chains. For example, thousands of ethene molecules join to make poly(ethene) - the plastic used in shopping bags.
The naming system is straightforward: just add 'poly' before the monomer name in brackets. So ethene becomes poly(ethene), and propene becomes poly(propene). Rubber is actually a natural polymer formed through addition polymerisation of plant molecules.
Remember: All addition polymerisation monomers must contain a C=C double bond, and no other products are formed - just the long polymer chain.
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Industrial Chemistry and Fertilisers
Plants need three essential elements to grow properly: nitrogen (N), phosphorus (P), and potassium (K) - that's why you'll see NPK on fertiliser packets. Any good fertiliser must contain at least one of these elements and be water-soluble so plant roots can absorb it.
The Haber process manufactures ammonia (NH₃) industrially by combining nitrogen and hydrogen gases. This reversible reaction uses high pressure and an iron catalyst to speed things up. It's economical because unreacted gases get recycled back through the system.
The Ostwald process then converts this ammonia into nitric acid (HNO₃). Ammonia gets oxidised to nitrogen monoxide using a platinum catalyst, then further oxidised to nitrogen dioxide, which dissolves in water to make nitric acid. This acid is crucial for making fertilisers like ammonium nitrate.
Industrial Insight: Both processes use catalysts to speed up reactions without being used up - platinum for the Ostwald process and iron for the Haber process.
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Radioactivity and Half-Life
Radioactive decay happens when unstable atomic nuclei break apart, releasing three types of radiation: alpha particles , beta particles (electrons), and gamma rays (electromagnetic waves). Each type has different penetrating power - paper stops alpha, aluminium stops beta, but you need thick concrete or lead to stop gamma rays.
Half-life is the time it takes for exactly half of a radioactive sample to decay. This rate is completely constant - nothing can speed it up or slow it down. If you start with 100g of a substance with a 14-day half-life, you'll have 50g after 14 days, 25g after 28 days, and so on.
Radioactivity has many practical uses in everyday life. Carbon-14 dating helps archaeologists determine the age of ancient organic materials, iodine-123 helps doctors detect thyroid problems, and americium-241 in smoke alarms detects particles from fires.
Safety Note: The penetrating power increases from alpha to gamma, but so does the difficulty in stopping the radiation - that's why different materials are needed for shielding.
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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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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