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Dejalee M
12/6/2025
Chemistry
Timeline of Atomic Theory
18
•
Dec 6, 2025
•
Dejalee M
@dejavu1110
The atomic theory has evolved dramatically over centuries, with scientists... Show more
The journey to understanding atoms began in ancient Greece around 400 BC with the Greek Model and has continued to evolve through modern times. John Dalton's Model in 1803 established the foundation for scientific atomic theory, treating atoms as indivisible particles.
J.J. Thompson's model in 1897 revealed that atoms contain smaller particles, introducing the concept of electrons. Ernest Rutherford's model in 1911 discovered the nucleus, revolutionizing our understanding of atomic structure.
Niels Bohr's Model in 1922 explained how electrons orbit the nucleus in specific energy levels. Finally, the wave model brought us to modern atomic theory, describing electrons as probability clouds rather than discrete particles.
Did you know? The word "atom" comes from the Greek word "atomos," meaning "indivisible" - though ironically, we now know atoms can be split into even smaller particles!
Democritus, a Greek philosopher, began investigating matter over 2,400 years ago. He questioned whether matter could be divided infinitely and named the smallest possible pieces "atomos." He described atoms as infinite in number, always moving, hard particles of different shapes and sizes made of the same material.
Unfortunately, Democritus' brilliant insights were ignored for over 2,000 years! Aristotle and Plato rejected his ideas, instead favoring an incorrect approach based on earth, air, water, and fire as the fundamental elements.
In the early 1800s, English chemist John Dalton revived and expanded atomic theory through scientific experiments. His groundbreaking theory stated that all elements consist of indivisible and indestructible atoms. He proposed that atoms of the same element are identical, while atoms of different elements have different properties. Dalton also explained that compounds form when atoms of different elements join together.
Think about it: Democritus developed a surprisingly accurate theory of atoms over 2,400 years ago with no scientific instruments—just pure reasoning and observation!
J.J. Thompson challenged Dalton's idea that atoms were indivisible when he discovered that atoms contain even smaller particles. His famous "Plum Pudding Model" proposed that atoms consisted of a positively charged substance with negatively charged electrons scattered throughout—like raisins in a pudding.
Thompson's breakthrough came while studying electric currents passing through gases. He observed rays of negatively charged particles (electrons) being emitted, which surprised him because the gas atoms themselves were neutral. This led him to conclude that these negative charges must come from within the atom itself.
Although Thompson correctly identified electrons, his model still had limitations. He knew atoms contained positive charges to balance the negative electrons, but he could never locate these positive particles. This mystery would eventually be solved by future scientists building on his work.
Connection: Thompson's discovery of the electron in 1897 was revolutionary—it was the first subatomic particle ever identified and completely changed how we understand matter!
The Bohr Model refined our understanding of atomic structure by proposing that electrons move in specific orbits. According to Bohr, these electron orbits exist at fixed distances from the nucleus, with each level having a defined energy state. This model helped explain why atoms emit specific light wavelengths when energized.
The Wave Model represents our modern understanding of atomic structure. Rather than treating electrons as tiny particles moving in fixed paths, it describes them using wave mechanics. In this model, electrons don't have exact locations—instead, we can only calculate the probability of finding an electron in a particular region.
This creates an electron cloud around the nucleus, where electrons exist in energy states rather than fixed positions. Higher-energy electrons tend to be found farther from the nucleus, while lower-energy electrons stay closer. This quantum mechanical view explains atomic behavior much more accurately than earlier models.
Mind-blower: According to the Wave Model, electrons don't orbit like planets around the sun—they exist as probability clouds where they might be found. This quantum weirdness is fundamental to how our universe works!
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.
App 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
Dejalee M
@dejavu1110
The atomic theory has evolved dramatically over centuries, with scientists building on each other's discoveries to understand the basic building blocks of matter. This timeline explores how our understanding of atoms progressed from ancient Greek philosophical ideas to the complex... Show more
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The journey to understanding atoms began in ancient Greece around 400 BC with the Greek Model and has continued to evolve through modern times. John Dalton's Model in 1803 established the foundation for scientific atomic theory, treating atoms as indivisible particles.
J.J. Thompson's model in 1897 revealed that atoms contain smaller particles, introducing the concept of electrons. Ernest Rutherford's model in 1911 discovered the nucleus, revolutionizing our understanding of atomic structure.
Niels Bohr's Model in 1922 explained how electrons orbit the nucleus in specific energy levels. Finally, the wave model brought us to modern atomic theory, describing electrons as probability clouds rather than discrete particles.
Did you know? The word "atom" comes from the Greek word "atomos," meaning "indivisible" - though ironically, we now know atoms can be split into even smaller particles!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Democritus, a Greek philosopher, began investigating matter over 2,400 years ago. He questioned whether matter could be divided infinitely and named the smallest possible pieces "atomos." He described atoms as infinite in number, always moving, hard particles of different shapes and sizes made of the same material.
Unfortunately, Democritus' brilliant insights were ignored for over 2,000 years! Aristotle and Plato rejected his ideas, instead favoring an incorrect approach based on earth, air, water, and fire as the fundamental elements.
In the early 1800s, English chemist John Dalton revived and expanded atomic theory through scientific experiments. His groundbreaking theory stated that all elements consist of indivisible and indestructible atoms. He proposed that atoms of the same element are identical, while atoms of different elements have different properties. Dalton also explained that compounds form when atoms of different elements join together.
Think about it: Democritus developed a surprisingly accurate theory of atoms over 2,400 years ago with no scientific instruments—just pure reasoning and observation!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
J.J. Thompson challenged Dalton's idea that atoms were indivisible when he discovered that atoms contain even smaller particles. His famous "Plum Pudding Model" proposed that atoms consisted of a positively charged substance with negatively charged electrons scattered throughout—like raisins in a pudding.
Thompson's breakthrough came while studying electric currents passing through gases. He observed rays of negatively charged particles (electrons) being emitted, which surprised him because the gas atoms themselves were neutral. This led him to conclude that these negative charges must come from within the atom itself.
Although Thompson correctly identified electrons, his model still had limitations. He knew atoms contained positive charges to balance the negative electrons, but he could never locate these positive particles. This mystery would eventually be solved by future scientists building on his work.
Connection: Thompson's discovery of the electron in 1897 was revolutionary—it was the first subatomic particle ever identified and completely changed how we understand matter!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The Bohr Model refined our understanding of atomic structure by proposing that electrons move in specific orbits. According to Bohr, these electron orbits exist at fixed distances from the nucleus, with each level having a defined energy state. This model helped explain why atoms emit specific light wavelengths when energized.
The Wave Model represents our modern understanding of atomic structure. Rather than treating electrons as tiny particles moving in fixed paths, it describes them using wave mechanics. In this model, electrons don't have exact locations—instead, we can only calculate the probability of finding an electron in a particular region.
This creates an electron cloud around the nucleus, where electrons exist in energy states rather than fixed positions. Higher-energy electrons tend to be found farther from the nucleus, while lower-energy electrons stay closer. This quantum mechanical view explains atomic behavior much more accurately than earlier models.
Mind-blower: According to the Wave Model, electrons don't orbit like planets around the sun—they exist as probability clouds where they might be found. This quantum weirdness is fundamental to how our universe works!
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.
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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
Algebra
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