Subjects
Biology
Chemistry
AP Chemistry
English
AP English Literature
Chemistry
Dec 5, 2025
491
3 pages
vi @vi0me
Ever wondered what makes up everything around you? Atoms are the tiny building blocks of all matter, and... Show more
Think of an atom as the smallest piece of an element that still acts like that element - it's literally the foundation of everything you can touch! Inside every atom, you'll find three main subatomic particles that work together like a perfectly balanced team.
The nucleus sits at the atom's centre, packed with protons and neutrons . Meanwhile, electrons (negative charge, almost no mass) whizz around the nucleus in shells. Here's the clever bit atoms always have equal numbers of protons and electrons, making them electrically neutral overall.
Every atom gets two important numbers that tell its story. The atomic number shows how many protons it has (like an element's ID card), whilst the mass number counts all the protons and neutrons together. For example, potassium has 19 protons and a mass number of 39.
Quick Tip Remember that nearly all an atom's mass comes from the nucleus - electrons are roughly 1,840 times lighter than protons!
Here's where atoms get interesting - isotopes are like different versions of the same element! They have identical numbers of protons (same element) but different numbers of neutrons, giving them different masses. It's like having the same car model but with different engine sizes.
Hydrogen-1 is the most common isotope of hydrogen, whilst carbon has several isotopes including carbon-12. The name always tells you the mass number - dead simple! Since electrons determine chemical properties, isotopes of the same element react identically despite having different masses.
Relative atomic mass is basically a weighted average that accounts for all an element's isotopes and their natural abundance. You'll find these values on the periodic table with the symbol Ar. The formula is (sum of isotope abundance × isotope mass number) ÷ (sum of all abundances).
Key Point Mass numbers are always whole numbers, but relative atomic masses often aren't because they're averages of different isotopes!
Mendeleev's periodic table was brilliant for its time - he arranged elements by increasing relative atomic mass and spotted repeating patterns (periodicity). He even left gaps for undiscovered elements and predicted their properties! The only hiccup was tellurium and iodine, which he had to swap based on their chemical properties rather than mass.
Today's modern periodic table arranges elements by atomic number (number of protons) rather than mass, solving Mendeleev's tellurium-iodine problem. Metals live on the left, non-metals on the right, with horizontal rows called periods and vertical columns called groups.
The journey from plum pudding model (1897) to nuclear atom was revolutionary. Rutherford's gold foil experiment (1905) showed that atoms are mostly empty space with a tiny, dense, positive nucleus. When alpha particles bounced back, it proved the nucleus was incredibly small but contained all the positive charge and most of the mass.
Bohr's model (1913) suggested electrons orbit in specific energy levels, explaining why different elements produce distinct flame colours. When electrons absorb energy, they jump to higher levels, then release light of definite frequencies when dropping back down.
Remember The nucleus is about 1/10,000th the size of the whole atom - imagine a marble in a football stadium!
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.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
27
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the evolution of atomic models, including the Bohr model and the concept of atomic particles. This summary covers key concepts such as atomic structure, electronic configurations, isotopes, and the historical development of atomic theory. Ideal for students seeking a comprehensive understanding of atomic structure.
ChemistryDiscovery of atoms to 1937
ChemistryBasics of Atoms and theory including atom history.
ChemistryExplore the fundamentals of atomic structure and the periodic table in this comprehensive summary. Understand key concepts such as atomic number, mass number, subatomic particles, and the classification of elements into groups. This resource covers the development of atomic models, the properties of noble gases, halogens, and alkali metals, as well as periodic trends in reactivity and physical properties. Ideal for students studying chemistry.
ChemistryStudy note about the electron configuration
ChemistryRadioactive chemicals, Decay, Nuclear Fission&Fusion
ChemistryApp 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
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
vi
@vi0me
Ever wondered what makes up everything around you? Atoms are the tiny building blocks of all matter, and understanding their structure is key to mastering chemistry. From discovering subatomic particles to organising the periodic table, you'll learn how scientists unlocked... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Think of an atom as the smallest piece of an element that still acts like that element - it's literally the foundation of everything you can touch! Inside every atom, you'll find three main subatomic particles that work together like a perfectly balanced team.
The nucleus sits at the atom's centre, packed with protons and neutrons . Meanwhile, electrons (negative charge, almost no mass) whizz around the nucleus in shells. Here's the clever bit: atoms always have equal numbers of protons and electrons, making them electrically neutral overall.
Every atom gets two important numbers that tell its story. The atomic number shows how many protons it has (like an element's ID card), whilst the mass number counts all the protons and neutrons together. For example, potassium has 19 protons and a mass number of 39.
Quick Tip: Remember that nearly all an atom's mass comes from the nucleus - electrons are roughly 1,840 times lighter than protons!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Here's where atoms get interesting - isotopes are like different versions of the same element! They have identical numbers of protons (same element) but different numbers of neutrons, giving them different masses. It's like having the same car model but with different engine sizes.
Hydrogen-1 is the most common isotope of hydrogen, whilst carbon has several isotopes including carbon-12. The name always tells you the mass number - dead simple! Since electrons determine chemical properties, isotopes of the same element react identically despite having different masses.
Relative atomic mass is basically a weighted average that accounts for all an element's isotopes and their natural abundance. You'll find these values on the periodic table with the symbol Ar. The formula is: (sum of isotope abundance × isotope mass number) ÷ (sum of all abundances).
Key Point: Mass numbers are always whole numbers, but relative atomic masses often aren't because they're averages of different isotopes!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Mendeleev's periodic table was brilliant for its time - he arranged elements by increasing relative atomic mass and spotted repeating patterns (periodicity). He even left gaps for undiscovered elements and predicted their properties! The only hiccup was tellurium and iodine, which he had to swap based on their chemical properties rather than mass.
Today's modern periodic table arranges elements by atomic number (number of protons) rather than mass, solving Mendeleev's tellurium-iodine problem. Metals live on the left, non-metals on the right, with horizontal rows called periods and vertical columns called groups.
The journey from plum pudding model (1897) to nuclear atom was revolutionary. Rutherford's gold foil experiment (1905) showed that atoms are mostly empty space with a tiny, dense, positive nucleus. When alpha particles bounced back, it proved the nucleus was incredibly small but contained all the positive charge and most of the mass.
Bohr's model (1913) suggested electrons orbit in specific energy levels, explaining why different elements produce distinct flame colours. When electrons absorb energy, they jump to higher levels, then release light of definite frequencies when dropping back down.
Remember: The nucleus is about 1/10,000th the size of the whole atom - imagine a marble in a football stadium!
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.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
27
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the evolution of atomic models, including the Bohr model and the concept of atomic particles. This summary covers key concepts such as atomic structure, electronic configurations, isotopes, and the historical development of atomic theory. Ideal for students seeking a comprehensive understanding of atomic structure.
ChemistryDiscovery of atoms to 1937
ChemistryBasics of Atoms and theory including atom history.
ChemistryExplore the fundamentals of atomic structure and the periodic table in this comprehensive summary. Understand key concepts such as atomic number, mass number, subatomic particles, and the classification of elements into groups. This resource covers the development of atomic models, the properties of noble gases, halogens, and alkali metals, as well as periodic trends in reactivity and physical properties. Ideal for students studying chemistry.
ChemistryStudy note about the electron configuration
ChemistryRadioactive chemicals, Decay, Nuclear Fission&Fusion
ChemistryApp 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
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
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