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Chemistry
7 Dec 2025
199
5 pages
The halogens are Group 7 elements that you'll find absolutely everywhere - from the fluoride in your toothpaste... Show more
Meet the halogens - one of the most important groups you'll study in chemistry! These elements include fluorine, chlorine, bromine, iodine, astatine and tennessine, though you'll mainly focus on the first four.
What makes halogens special is their 7 outer shell electrons. This means they're just one electron away from having a complete outer shell, which explains why they're so desperate to react with other elements.
Quick Tip Remember that halogens are all non-metals, making them quite different from the metals you'll find on the left side of the periodic table.
Since halogens have 7 outer shell electrons, they're incredibly reactive - always trying to grab that one extra electron to complete their outer shell. When they succeed, they form 1- ions (negatively charged particles).
You'll notice that halogen atoms are diatomic, meaning they naturally pair up with themselves. So instead of finding single fluorine atoms, you'll see F₂, Cl₂, Br₂, and so on.
This electron-grabbing behaviour makes halogens brilliant at forming compounds. They'll bond with pretty much anything that's willing to share or give up electrons!
Remember The closer a halogen is to having 8 outer electrons, the more reactive it becomes - it's like being one step away from your goal!
Halogens are fantastic at making two types of bonds, depending on what they're reacting with. With non-metals, they form covalent bonds by sharing electrons. With metals, they create ionic bonds by stealing electrons completely.
The key to understanding halogen reactions is remembering they gain one electron to fill their outer shell. This makes them incredibly predictable - they almost always want to become 1- ions.
Because they're so close to having full outer shells, halogens react quickly and often dramatically. This is why chlorine gas is dangerous, but it's also why these elements are so useful in everyday products.
Study Hack If you can remember "7 electrons = wants 1 more", you'll understand most halogen behaviour instantly!
Here's where halogens get really interesting - their reactivity decreases as you go down the group. Fluorine (at the top) is incredibly reactive, while iodine (further down) is much calmer.
This happens because atom size increases down the group. Larger atoms mean the outer electrons are further from the nucleus, so there's weaker attraction between them. It becomes harder for bigger atoms to attract that extra electron they need.
Meanwhile, melting and boiling points increase going down the group. This is because larger atoms have stronger intermolecular forces between them.
Memory Trick Think of it like a magnet - the further away you are, the weaker the pull becomes!
Halogens follow clear bonding rules covalent bonds with non-metals and ionic bonds with metals. This makes predicting their behaviour much easier once you know what they're reacting with.
The most important reaction type you'll encounter is displacement reactions. More reactive halogens (higher up the group) can kick out less reactive ones from their compounds. It's like a chemical version of "survival of the fittest"!
For example, fluorine + sodium chloride → sodium fluoride + chlorine. The fluorine muscles in and displaces the chlorine because it's more reactive.
Exam Tip In displacement reactions, always check which halogen is higher up the group - that's your winner!
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.
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ChemistryThese notes help inform you on the basics of Chemistry and get you used to the terms used in this subject.
ChemistryThis content contains atoms and elements, ion isotopes, and bonds
ChemistryAtomic Radius & Ionization Energy
ChemistryUnderstanding the location and movement of electrons within the atomic structure based on probability maps and orbital regions.
Chemistrythis is the study guide i made for myself for chem this year :) hopefully it helps
ChemistryQuotes from every main character
English LiteratureApp Store
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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
The halogens are Group 7 elements that you'll find absolutely everywhere - from the fluoride in your toothpaste to the chlorine in swimming pools. These incredibly reactive non-metals follow predictable patterns that make chemistry much easier once you understand the... Show more
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Meet the halogens - one of the most important groups you'll study in chemistry! These elements include fluorine, chlorine, bromine, iodine, astatine and tennessine, though you'll mainly focus on the first four.
What makes halogens special is their 7 outer shell electrons. This means they're just one electron away from having a complete outer shell, which explains why they're so desperate to react with other elements.
Quick Tip: Remember that halogens are all non-metals, making them quite different from the metals you'll find on the left side of the periodic table.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Since halogens have 7 outer shell electrons, they're incredibly reactive - always trying to grab that one extra electron to complete their outer shell. When they succeed, they form 1- ions (negatively charged particles).
You'll notice that halogen atoms are diatomic, meaning they naturally pair up with themselves. So instead of finding single fluorine atoms, you'll see F₂, Cl₂, Br₂, and so on.
This electron-grabbing behaviour makes halogens brilliant at forming compounds. They'll bond with pretty much anything that's willing to share or give up electrons!
Remember: The closer a halogen is to having 8 outer electrons, the more reactive it becomes - it's like being one step away from your goal!
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Halogens are fantastic at making two types of bonds, depending on what they're reacting with. With non-metals, they form covalent bonds by sharing electrons. With metals, they create ionic bonds by stealing electrons completely.
The key to understanding halogen reactions is remembering they gain one electron to fill their outer shell. This makes them incredibly predictable - they almost always want to become 1- ions.
Because they're so close to having full outer shells, halogens react quickly and often dramatically. This is why chlorine gas is dangerous, but it's also why these elements are so useful in everyday products.
Study Hack: If you can remember "7 electrons = wants 1 more", you'll understand most halogen behaviour instantly!
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Improve your grades
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Here's where halogens get really interesting - their reactivity decreases as you go down the group. Fluorine (at the top) is incredibly reactive, while iodine (further down) is much calmer.
This happens because atom size increases down the group. Larger atoms mean the outer electrons are further from the nucleus, so there's weaker attraction between them. It becomes harder for bigger atoms to attract that extra electron they need.
Meanwhile, melting and boiling points increase going down the group. This is because larger atoms have stronger intermolecular forces between them.
Memory Trick: Think of it like a magnet - the further away you are, the weaker the pull becomes!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Halogens follow clear bonding rules: covalent bonds with non-metals and ionic bonds with metals. This makes predicting their behaviour much easier once you know what they're reacting with.
The most important reaction type you'll encounter is displacement reactions. More reactive halogens (higher up the group) can kick out less reactive ones from their compounds. It's like a chemical version of "survival of the fittest"!
For example, fluorine + sodium chloride → sodium fluoride + chlorine. The fluorine muscles in and displaces the chlorine because it's more reactive.
Exam Tip: In displacement reactions, always check which halogen is higher up the group - that's your winner!
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.
5
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Lewis dot structures how to with examples
ChemistryThese notes help inform you on the basics of Chemistry and get you used to the terms used in this subject.
ChemistryThis content contains atoms and elements, ion isotopes, and bonds
ChemistryAtomic Radius & Ionization Energy
ChemistryUnderstanding the location and movement of electrons within the atomic structure based on probability maps and orbital regions.
Chemistrythis is the study guide i made for myself for chem this year :) hopefully it helps
ChemistryQuotes from every main character
English LiteratureApp 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