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flo
03/12/2025
Chemistry
CHEMISTRY
86
•
3 Dec 2025
•
Understanding Basic Chemistry Concepts
flo
@flo_effins
1 / 4
Chemistry Fundamentals and Atomic Structure
Getting your head around the basic definitions is crucial for chemistry success. An element is simply a substance made of one type of atom, like pure gold or oxygen. When two or more different elements get chemically joined together, you've got a compound - think water .
Mixtures are different because the substances aren't chemically joined, so you can actually separate them again. A molecule forms when two or more non-metal elements join together - like the oxygen molecules you're breathing right now.
The periodic table is organised in a clever way that makes chemistry much easier. Groups are the vertical columns, and periods are the horizontal rows. Elements in the same group behave similarly, which is dead useful for predicting reactions.
Remember: If substances are chemically joined = compound. If they're just mixed together = mixture!
History of the Periodic Table and Atomic Structure
Four brilliant scientists gradually figured out how to organise the elements properly. John Dalton (1808) started by arranging elements by atomic weight. Johann Dobereiner (1817) tried grouping elements in threes, but it didn't work for everything.
John Newlands (1864) spotted that every 8th element had similar properties - his 'table of octaves'. Finally, Dimitri Mendeleev (1869) cracked it by leaving gaps for undiscovered elements and sometimes swapping the order to make patterns work.
Understanding atomic structure is straightforward once you know the basics. Protons and neutrons hang out in the nucleus (centre), while electrons orbit around the outside in shells. The relative atomic mass is just protons plus neutrons added together.
Isotopes are atoms of the same element with different numbers of neutrons. They have the same chemical properties but different masses - like having the same personality but different weights.
Top Tip: Elements in the same group have the same number of outer electrons, which explains why they behave so similarly!
Group 7 (Halogens) and Group 1 Properties
Group 7 elements are called the halogens, and they're pretty reactive bunch. Chlorine (green gas) sterilises water, bromine (orange liquid) makes pesticides, and iodine (grey solid) sterilises wounds. They all form salts when they react with metals.
Here's the weird bit - halogens get more reactive going up the group, with fluorine being the most reactive. Smaller atoms find it easier to grab electrons from other atoms because there's less distance involved.
Displacement reactions happen when a more reactive element kicks out a less reactive one from its compound. It's like queue-jumping in chemistry - the more reactive element always wins.
Group 1 metals (alkali metals) react vigorously with water, producing hydrogen gas and metal hydroxides. Unlike the halogens, Group 1 reactivity increases going down because the outer electron gets further from the nucleus and becomes easier to lose.
Memory Trick: Halogens - smaller = more reactive. Alkali metals - bigger = more reactive!
Transition Metals and Noble Gases
Transition metals are the workhorses of the periodic table - they're brilliant conductors of heat and electricity, which makes them perfect for wiring and cookware. They're malleable (you can hammer them into shape) and have high melting points plus high density.
These properties make transition metals incredibly useful in industry. You'll find them in everything from car parts to jewellery because they're strong, durable, and look good too.
Noble gases are the opposite - they're so unreactive they're called 'inert'. This makes them perfect for creating safe atmospheres during welding or protecting valuable specimens. You see them lighting up our world in neon signs and krypton headlights.
Understanding states of matter is simple: solids melt and boil above room temperature, liquids melt below room temperature but boil above it, and gases do both below room temperature.
Quick Check: If you can bend it and it conducts electricity well, it's probably a transition metal!
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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
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Best app on earth! no words because it’s too good
Thomas R
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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
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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.
David K
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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 Basic Chemistry Concepts
flo
@flo_effins
Chemistry might seem overwhelming at first, but it's basically about understanding the building blocks of everything around us. This revision guide covers the fundamentals you need to know about elements, compounds, and how scientists organised them into the periodic table... Show more
Chemistry Fundamentals and Atomic Structure
Getting your head around the basic definitions is crucial for chemistry success. An element is simply a substance made of one type of atom, like pure gold or oxygen. When two or more different elements get chemically joined together, you've got a compound - think water .
Mixtures are different because the substances aren't chemically joined, so you can actually separate them again. A molecule forms when two or more non-metal elements join together - like the oxygen molecules you're breathing right now.
The periodic table is organised in a clever way that makes chemistry much easier. Groups are the vertical columns, and periods are the horizontal rows. Elements in the same group behave similarly, which is dead useful for predicting reactions.
Remember: If substances are chemically joined = compound. If they're just mixed together = mixture!
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Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
History of the Periodic Table and Atomic Structure
Four brilliant scientists gradually figured out how to organise the elements properly. John Dalton (1808) started by arranging elements by atomic weight. Johann Dobereiner (1817) tried grouping elements in threes, but it didn't work for everything.
John Newlands (1864) spotted that every 8th element had similar properties - his 'table of octaves'. Finally, Dimitri Mendeleev (1869) cracked it by leaving gaps for undiscovered elements and sometimes swapping the order to make patterns work.
Understanding atomic structure is straightforward once you know the basics. Protons and neutrons hang out in the nucleus (centre), while electrons orbit around the outside in shells. The relative atomic mass is just protons plus neutrons added together.
Isotopes are atoms of the same element with different numbers of neutrons. They have the same chemical properties but different masses - like having the same personality but different weights.
Top Tip: Elements in the same group have the same number of outer electrons, which explains why they behave so similarly!
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Group 7 (Halogens) and Group 1 Properties
Group 7 elements are called the halogens, and they're pretty reactive bunch. Chlorine (green gas) sterilises water, bromine (orange liquid) makes pesticides, and iodine (grey solid) sterilises wounds. They all form salts when they react with metals.
Here's the weird bit - halogens get more reactive going up the group, with fluorine being the most reactive. Smaller atoms find it easier to grab electrons from other atoms because there's less distance involved.
Displacement reactions happen when a more reactive element kicks out a less reactive one from its compound. It's like queue-jumping in chemistry - the more reactive element always wins.
Group 1 metals (alkali metals) react vigorously with water, producing hydrogen gas and metal hydroxides. Unlike the halogens, Group 1 reactivity increases going down because the outer electron gets further from the nucleus and becomes easier to lose.
Memory Trick: Halogens - smaller = more reactive. Alkali metals - bigger = more reactive!
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Transition Metals and Noble Gases
Transition metals are the workhorses of the periodic table - they're brilliant conductors of heat and electricity, which makes them perfect for wiring and cookware. They're malleable (you can hammer them into shape) and have high melting points plus high density.
These properties make transition metals incredibly useful in industry. You'll find them in everything from car parts to jewellery because they're strong, durable, and look good too.
Noble gases are the opposite - they're so unreactive they're called 'inert'. This makes them perfect for creating safe atmospheres during welding or protecting valuable specimens. You see them lighting up our world in neon signs and krypton headlights.
Understanding states of matter is simple: solids melt and boil above room temperature, liquids melt below room temperature but boil above it, and gases do both below room temperature.
Quick Check: If you can bend it and it conducts electricity well, it's probably a transition metal!
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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4.9/5
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4.8/5
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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