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Corah
14/12/2025
Chemistry
Chemistry: Elements, Compounds, and Mixtures
100
•
14 Dec 2025
•
Understanding Chemistry: Atoms, Molecules, Compounds, and Mixtures
Corah
@corahbretton
1 / 4
The Basics of Matter
Everything you see is made of atoms - think of them as nature's building blocks. When atoms team up, they form molecules, and this is where chemistry gets interesting.
Compounds are formed when two or more different elements join forces chemically - like sodium and chlorine creating table salt. Mixtures, on the other hand, are just substances hanging out together without any chemical commitment, like oil and water.
Here's a golden rule that'll save you in exams: conservation of mass means the mass of what you start with always equals the mass of what you end up with. No atoms disappear - they just rearrange themselves.
Pro tip: When balancing equations, count atoms on both sides like you're checking your maths - they should always match up perfectly.
Inside the Atom
Atoms are incredibly tiny - about 1 × 10⁻¹⁰ metres across, which means you could fit millions across the width of a human hair. The nucleus at the centre is 10,000 times smaller than the whole atom, yet contains nearly all its mass.
Every atom has an atomic number (number of protons) that determines what element it is. The mass number tells you the total protons plus neutrons. Think of protons as an element's ID card - hydrogen always has 1, helium always has 2.
Isotopes are like identical twins with different weights - same element, same number of protons, but different numbers of neutrons. Carbon-12 and carbon-13 are perfect examples, both carbon but with slightly different masses.
Remember: The number of protons never changes for an element - that's what makes carbon always carbon and oxygen always oxygen.
Chemical Bonding
Compounds form when elements get together and actually bond chemically - it's like they're getting married rather than just dating. This happens through electrons being shared, given, or taken between atoms.
Ionic bonding occurs between metals and non-metals. The metal loses electrons (becoming positive), whilst the non-metal gains them (becoming negative). These opposite charges attract like magnets - think sodium chloride or magnesium oxide.
Covalent bonding happens when non-metals share electrons, creating molecules. Water, carbon monoxide, and nitrogen chloride are classic examples where atoms team up by sharing rather than transferring electrons.
Quick check: Metal + non-metal = ionic bonding, whilst non-metal + non-metal = covalent bonding.
Separation Techniques and Atomic History
Scientists use different tricks to separate mixtures: crystallisation for getting solids from solutions, distillation for separating liquids with different boiling points, and chromatography for substances that dissolve differently.
The story of atomic discovery is brilliant. John Dalton imagined atoms as tiny, indivisible spheres. J.J. Thompson suggested the plum pudding model - a positive ball with electrons stuck in it like raisins.
Rutherford's alpha scattering experiment changed everything. By firing particles at gold foil, he discovered that atoms are mostly empty space with a tiny, dense nucleus. Niels Bohr then proposed that electrons orbit in specific energy levels or shells.
Fun fact: Most alpha particles went straight through the gold foil, proving atoms are mostly empty space - you're basically made of nothing!
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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
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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
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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 Chemistry: Atoms, Molecules, Compounds, and Mixtures
Corah
@corahbretton
Chemistry might seem daunting, but it's actually all around you - from the water you drink to the air you breathe. This chapter covers the fundamental building blocks of matter and how scientists figured out what atoms really look like... Show more
The Basics of Matter
Everything you see is made of atoms - think of them as nature's building blocks. When atoms team up, they form molecules, and this is where chemistry gets interesting.
Compounds are formed when two or more different elements join forces chemically - like sodium and chlorine creating table salt. Mixtures, on the other hand, are just substances hanging out together without any chemical commitment, like oil and water.
Here's a golden rule that'll save you in exams: conservation of mass means the mass of what you start with always equals the mass of what you end up with. No atoms disappear - they just rearrange themselves.
Pro tip: When balancing equations, count atoms on both sides like you're checking your maths - they should always match up perfectly.
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Inside the Atom
Atoms are incredibly tiny - about 1 × 10⁻¹⁰ metres across, which means you could fit millions across the width of a human hair. The nucleus at the centre is 10,000 times smaller than the whole atom, yet contains nearly all its mass.
Every atom has an atomic number (number of protons) that determines what element it is. The mass number tells you the total protons plus neutrons. Think of protons as an element's ID card - hydrogen always has 1, helium always has 2.
Isotopes are like identical twins with different weights - same element, same number of protons, but different numbers of neutrons. Carbon-12 and carbon-13 are perfect examples, both carbon but with slightly different masses.
Remember: The number of protons never changes for an element - that's what makes carbon always carbon and oxygen always oxygen.
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By signing up you accept Terms of Service and Privacy Policy
Chemical Bonding
Compounds form when elements get together and actually bond chemically - it's like they're getting married rather than just dating. This happens through electrons being shared, given, or taken between atoms.
Ionic bonding occurs between metals and non-metals. The metal loses electrons (becoming positive), whilst the non-metal gains them (becoming negative). These opposite charges attract like magnets - think sodium chloride or magnesium oxide.
Covalent bonding happens when non-metals share electrons, creating molecules. Water, carbon monoxide, and nitrogen chloride are classic examples where atoms team up by sharing rather than transferring electrons.
Quick check: Metal + non-metal = ionic bonding, whilst non-metal + non-metal = covalent bonding.
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Separation Techniques and Atomic History
Scientists use different tricks to separate mixtures: crystallisation for getting solids from solutions, distillation for separating liquids with different boiling points, and chromatography for substances that dissolve differently.
The story of atomic discovery is brilliant. John Dalton imagined atoms as tiny, indivisible spheres. J.J. Thompson suggested the plum pudding model - a positive ball with electrons stuck in it like raisins.
Rutherford's alpha scattering experiment changed everything. By firing particles at gold foil, he discovered that atoms are mostly empty space with a tiny, dense nucleus. Niels Bohr then proposed that electrons orbit in specific energy levels or shells.
Fun fact: Most alpha particles went straight through the gold foil, proving atoms are mostly empty space - you're basically made of nothing!
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
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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Most popular content: Molecules and Compounds
Most popular content in Chemistry
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
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