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Dec 5, 2025
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Comprehensive Review of Periodic Table Trends and Atomic Properties
Shreya Bedi
@shreyabedi_oyaa
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Polyatomic Ions and Ionic Compounds
Polyatomic ions are charged particles made of multiple atoms that act as a single unit. Some common ones include ammonium (NH₄⁺), hydroxide (OH⁻), nitrate (NO₃⁻), and sulfate (SO₄²⁻). You'll need to memorize these for your chemistry class!
When forming ionic compounds, we combine positive ions (cations) and negative ions (anions) to create neutral compounds. The key is to balance the charges. For example, when combining sodium (Na⁺) with hydroxide (OH⁻), we get NaOH because the charges balance out .
For ions with multiple charges, we need to adjust the ratios. When magnesium (Mg²⁺) combines with acetate (C₂H₃O₂⁻), we need two acetate ions to balance magnesium's 2+ charge, giving us Mg(C₂H₃O₂)₂. The parentheses indicate that the entire polyatomic ion repeats.
💡 Quick Tip: When forming ionic compounds, cross the charges to find the subscripts. For example, Ca²⁺ and Cl⁻ form CaCl₂ because you need two Cl⁻ ions to balance the 2+ charge.
Breaking Down Compounds and Naming Conventions
Breaking down compounds is like reverse-engineering a formula. For example, ZnO breaks down to Zn²⁺ + O²⁻, while more complex compounds like Fe₂(SO₄)₃ break down to 2Fe³⁺ + 3(SO₄²⁻). The key is ensuring the overall charge equals zero.
Compounds can be either ionic or covalent, and they follow different naming rules. Ionic compounds typically involve a metal and a nonmetal, like Na₂CO₃ (sodium carbonate). Covalent compounds usually form between nonmetals, like P₂O₅ (diphosphorus pentoxide).
For ionic compounds, name the cation first (usually a metal), then the anion. For covalent compounds, use prefixes to indicate the number of atoms. SiO₂ is silicon dioxide because there are two oxygen atoms.
📝 Remember: Transition metals often have Roman numerals in their names (like iron(II) or iron(III)) to indicate their charge, since these metals can form different charges in compounds.
Writing Chemical Formulas
Converting between names and formulas is a critical chemistry skill. For covalent compounds like dinitrogen trioxide, the prefixes tell you exactly how many atoms to include—N₂O₃ has two nitrogen and three oxygen atoms.
For ionic compounds, you need to balance the charges. Lithium acetate combines Li⁺ with CH₃COO⁻ to form LiCH₃COO because their charges balance out. More complex examples include aluminum hydroxide, which combines Al³⁺ with three OH⁻ ions to form Al(OH)₃.
When metals can have multiple charges (like vanadium), the Roman numeral in the name tells you which charge to use. Vanadium(V) oxide means vanadium has a 5+ charge, so it would combine with oxygen (O²⁻) to form V₂O₅.
⚡ Master This: Create flashcards for common polyatomic ions and their charges. Being able to quickly recognize ions like PO₄³⁻ (phosphate) or SO₄²⁻ (sulfate) will save you tons of time when writing chemical formulas.
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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.
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I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
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Brad T
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Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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!
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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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I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
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Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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
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This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Comprehensive Review of Periodic Table Trends and Atomic Properties
Shreya Bedi
@shreyabedi_oyaa
Chemistry gets a lot more interesting when we start looking at how atoms combine into compounds. This guide covers polyatomic ions, ionic compounds, and naming conventions that will help you ace your next chemistry test. Understanding these concepts is essential... Show more
Polyatomic Ions and Ionic Compounds
Polyatomic ions are charged particles made of multiple atoms that act as a single unit. Some common ones include ammonium (NH₄⁺), hydroxide (OH⁻), nitrate (NO₃⁻), and sulfate (SO₄²⁻). You'll need to memorize these for your chemistry class!
When forming ionic compounds, we combine positive ions (cations) and negative ions (anions) to create neutral compounds. The key is to balance the charges. For example, when combining sodium (Na⁺) with hydroxide (OH⁻), we get NaOH because the charges balance out .
For ions with multiple charges, we need to adjust the ratios. When magnesium (Mg²⁺) combines with acetate (C₂H₃O₂⁻), we need two acetate ions to balance magnesium's 2+ charge, giving us Mg(C₂H₃O₂)₂. The parentheses indicate that the entire polyatomic ion repeats.
💡 Quick Tip: When forming ionic compounds, cross the charges to find the subscripts. For example, Ca²⁺ and Cl⁻ form CaCl₂ because you need two Cl⁻ ions to balance the 2+ charge.
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Breaking Down Compounds and Naming Conventions
Breaking down compounds is like reverse-engineering a formula. For example, ZnO breaks down to Zn²⁺ + O²⁻, while more complex compounds like Fe₂(SO₄)₃ break down to 2Fe³⁺ + 3(SO₄²⁻). The key is ensuring the overall charge equals zero.
Compounds can be either ionic or covalent, and they follow different naming rules. Ionic compounds typically involve a metal and a nonmetal, like Na₂CO₃ (sodium carbonate). Covalent compounds usually form between nonmetals, like P₂O₅ (diphosphorus pentoxide).
For ionic compounds, name the cation first (usually a metal), then the anion. For covalent compounds, use prefixes to indicate the number of atoms. SiO₂ is silicon dioxide because there are two oxygen atoms.
📝 Remember: Transition metals often have Roman numerals in their names (like iron(II) or iron(III)) to indicate their charge, since these metals can form different charges in compounds.
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Writing Chemical Formulas
Converting between names and formulas is a critical chemistry skill. For covalent compounds like dinitrogen trioxide, the prefixes tell you exactly how many atoms to include—N₂O₃ has two nitrogen and three oxygen atoms.
For ionic compounds, you need to balance the charges. Lithium acetate combines Li⁺ with CH₃COO⁻ to form LiCH₃COO because their charges balance out. More complex examples include aluminum hydroxide, which combines Al³⁺ with three OH⁻ ions to form Al(OH)₃.
When metals can have multiple charges (like vanadium), the Roman numeral in the name tells you which charge to use. Vanadium(V) oxide means vanadium has a 5+ charge, so it would combine with oxygen (O²⁻) to form V₂O₅.
⚡ Master This: Create flashcards for common polyatomic ions and their charges. Being able to quickly recognize ions like PO₄³⁻ (phosphate) or SO₄²⁻ (sulfate) will save you tons of time when writing chemical formulas.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the 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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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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user