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Feb 10, 2026
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Understanding Chemical Nomenclature
nick
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Binary Ionic Compounds & The Stock System
Ever wonder how chemists name all those chemical compounds? It's not as complicated as it seems! For binary ionic compounds (made of a metal cation and a nonmetal anion), the metal is named first, followed by the nonmetal with its ending changed to "-ide."
When transition metals are involved, we use the Stock System with Roman numerals to show the metal's charge. For example, FeCl₃ is named "iron(III) chloride" because iron has a +3 charge. Some transition metals can form multiple ions (like Cu⁺ and Cu²⁺), which is why specifying the charge is important.
To write formulas for ionic compounds, remember that the overall charge must be neutral. Use the "crisscross method" where the numerical value of each ion's charge becomes the subscript for the other ion. For example, aluminum oxide (Al³⁺ and O²⁻) becomes Al₂O₃.
Chemistry Tip: When you see a compound like KF or CaBr₂, the subscripts in the formula don't affect the name - they just tell you how many atoms are needed to balance the charges. Potassium fluoride is still potassium fluoride whether it's written as KF, K₂F₂, or K₃F₃!
Polyatomic ions are groups of atoms that act as a single unit with an overall charge. Most polyatomic ions are anions and often end in "-ate" or "-ite" (like nitrate NO₃⁻ or nitrite NO₂⁻). The most common polyatomic cation is ammonium (NH₄⁺).
Polyatomic Ions & Molecular Compounds
Transition metals form ions by losing electrons from their outer s-orbitals first. This is why they can form multiple different ion charges - they have unfilled inner d-electron shells that can also lose electrons.
Ternary ionic compounds contain three or more elements, usually with one type of cation and one type of anion, where at least one is a polyatomic ion. For example, NH₄Cl (ammonium chloride) or Fe(OH)₃ (iron(III) hydroxide). When writing formulas with polyatomic ions, use parentheses and a subscript to show how many of those ions are present.
For binary molecular compounds (made of two nonmetals), we use a prefix system to show how many atoms of each element are present. The first element doesn't use "mono-" but the second does (for one atom). For example, NO is nitrogen monoxide, and Cl₂O₇ is dichlorine heptoxide.
Remember this! Ionic compounds form between metals and nonmetals, while molecular compounds form between nonmetals only. This distinction helps you know which naming system to use.
Acids are molecular compounds that release H⁺ when dissolved in water. Binary acids are named "hydro-[element]ic acid" like hydrochloric acid (HCl). Oxoacids follow a pattern based on their related polyatomic ions: "-ate" becomes "-ic acid" and "-ite" becomes "-ous acid."
Bases produce hydroxide ions (OH⁻) in water and are named by writing the cation first, followed by "hydroxide." Common examples include calcium hydroxide Ca(OH)₂ and ammonium hydroxide NH₄OH.
Atomic Ions & Periodic Table Trends
Looking at the periodic table reveals patterns in how elements form ions. This visual guide shows the most common ion charges for elements across the table.
Group 1A (alkali metals) form +1 ions (like Na⁺), while Group 2A (alkaline earth metals) form +2 ions (like Ca²⁺). This makes sense because these elements want to lose their outer electrons to achieve a stable electron configuration.
On the right side of the table, Group 7A (halogens) typically form -1 ions (like Cl⁻), and Group 6A elements usually form -2 ions (like O²⁻). These elements gain electrons to fill their outer shells.
Transition metals in the middle of the table can form multiple ion charges. For instance, iron can form Fe²⁺ and Fe³⁺ ions. That's why we need the Stock System with Roman numerals to specify which ion we're talking about.
Quick Check: Notice how the charge of an ion often matches its group number or is calculated as for nonmetals on the right side of the table. This pattern can help you predict ion charges!
Understanding these patterns makes it much easier to predict how elements will combine to form compounds, and how to name those compounds correctly.
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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
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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
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.
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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
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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.😋🩷🎀
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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
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Understanding Chemical Nomenclature
nick
@nramos
Chemical nomenclature helps you name compounds properly and write their formulas accurately. Understanding the rules for naming ionic, molecular compounds, and acids is essential for success in chemistry class and on your exams.
Binary Ionic Compounds & The Stock System
Ever wonder how chemists name all those chemical compounds? It's not as complicated as it seems! For binary ionic compounds (made of a metal cation and a nonmetal anion), the metal is named first, followed by the nonmetal with its ending changed to "-ide."
When transition metals are involved, we use the Stock System with Roman numerals to show the metal's charge. For example, FeCl₃ is named "iron(III) chloride" because iron has a +3 charge. Some transition metals can form multiple ions (like Cu⁺ and Cu²⁺), which is why specifying the charge is important.
To write formulas for ionic compounds, remember that the overall charge must be neutral. Use the "crisscross method" where the numerical value of each ion's charge becomes the subscript for the other ion. For example, aluminum oxide (Al³⁺ and O²⁻) becomes Al₂O₃.
Chemistry Tip: When you see a compound like KF or CaBr₂, the subscripts in the formula don't affect the name - they just tell you how many atoms are needed to balance the charges. Potassium fluoride is still potassium fluoride whether it's written as KF, K₂F₂, or K₃F₃!
Polyatomic ions are groups of atoms that act as a single unit with an overall charge. Most polyatomic ions are anions and often end in "-ate" or "-ite" (like nitrate NO₃⁻ or nitrite NO₂⁻). The most common polyatomic cation is ammonium (NH₄⁺).
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Polyatomic Ions & Molecular Compounds
Transition metals form ions by losing electrons from their outer s-orbitals first. This is why they can form multiple different ion charges - they have unfilled inner d-electron shells that can also lose electrons.
Ternary ionic compounds contain three or more elements, usually with one type of cation and one type of anion, where at least one is a polyatomic ion. For example, NH₄Cl (ammonium chloride) or Fe(OH)₃ (iron(III) hydroxide). When writing formulas with polyatomic ions, use parentheses and a subscript to show how many of those ions are present.
For binary molecular compounds (made of two nonmetals), we use a prefix system to show how many atoms of each element are present. The first element doesn't use "mono-" but the second does (for one atom). For example, NO is nitrogen monoxide, and Cl₂O₇ is dichlorine heptoxide.
Remember this! Ionic compounds form between metals and nonmetals, while molecular compounds form between nonmetals only. This distinction helps you know which naming system to use.
Acids are molecular compounds that release H⁺ when dissolved in water. Binary acids are named "hydro-[element]ic acid" like hydrochloric acid (HCl). Oxoacids follow a pattern based on their related polyatomic ions: "-ate" becomes "-ic acid" and "-ite" becomes "-ous acid."
Bases produce hydroxide ions (OH⁻) in water and are named by writing the cation first, followed by "hydroxide." Common examples include calcium hydroxide Ca(OH)₂ and ammonium hydroxide NH₄OH.
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Atomic Ions & Periodic Table Trends
Looking at the periodic table reveals patterns in how elements form ions. This visual guide shows the most common ion charges for elements across the table.
Group 1A (alkali metals) form +1 ions (like Na⁺), while Group 2A (alkaline earth metals) form +2 ions (like Ca²⁺). This makes sense because these elements want to lose their outer electrons to achieve a stable electron configuration.
On the right side of the table, Group 7A (halogens) typically form -1 ions (like Cl⁻), and Group 6A elements usually form -2 ions (like O²⁻). These elements gain electrons to fill their outer shells.
Transition metals in the middle of the table can form multiple ion charges. For instance, iron can form Fe²⁺ and Fe³⁺ ions. That's why we need the Stock System with Roman numerals to specify which ion we're talking about.
Quick Check: Notice how the charge of an ion often matches its group number or is calculated as for nonmetals on the right side of the table. This pattern can help you predict ion charges!
Understanding these patterns makes it much easier to predict how elements will combine to form compounds, and how to name those compounds correctly.
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?
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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 Knowunity AI. 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 Knowunity AI. 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