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Evolution of Atomic Models
The way we understand atoms has changed dramatically over time. It all started with Democritus's Spherical Model, which imagined atoms as tiny, indivisible spheres. John Dalton expanded this by stating atoms are neither created nor destroyed during chemical reactions.
As technology advanced, so did our understanding. Thomson's Plum Pudding Model suggested atoms were positive spheres with negative electrons embedded throughout. This was overturned by Rutherford's Nuclear Model, which discovered that atoms have a concentrated, positive nucleus with mostly empty space around it.
Bohr's Planetary Model represented a major breakthrough, proposing that electrons orbit the nucleus in specific energy levels, similar to planets orbiting the sun. Finally, the Quantum Mechanical Model by Schrödinger revolutionized our understanding by describing electrons as waves with probabilistic locations rather than definite particles.
Remember This! Atomic theory explains important laws like Conservation of Mass (matter cannot be created or destroyed) and Definite Composition (elements combine in predictable ratios to form compounds).
Quantum Theory and the Periodic Table
Quantum theory helped explain mysteries that previous atomic models couldn't. Einstein showed that light behaves as particles called photons, while de Broglie demonstrated that matter can behave like waves—a concept called wave-particle duality.
The location and behavior of electrons is described by four quantum numbers: principal (n), angular momentum (l), magnetic (mₗ), and spin (mₛ). These numbers follow important rules like Pauli's Exclusion Principle (no two electrons can have identical quantum numbers) and Hund's Rule (electrons occupy orbitals singly before pairing up).
The periodic table organizes elements based on their properties and electron arrangements. Elements are arranged in groups (vertical columns) and periods (horizontal rows). Groups share similar chemical properties because they have the same number of valence electrons. For example, Group IA elements (alkali metals) all have one valence electron and are highly reactive, while Group VIIIA (noble gases) have full outer shells and rarely react.
Fun Fact: Dmitri Mendeleev created the first widely accepted periodic table in 1869, leaving gaps for elements that hadn't been discovered yet. His predictions about these unknown elements turned out to be amazingly accurate!
Periodic Trends and Chemical Bonds
Elements show predictable patterns across the periodic table. Atomic radius generally decreases across a period and increases down a group. Electronegativity (how strongly atoms attract electrons) increases across a period and decreases down a group, which helps predict how elements will bond.
When atoms interact, they form chemical bonds. Ionic bonds occur when electrons transfer completely between atoms, typically from a metal to a non-metal, creating charged ions that attract each other. Covalent bonds involve atoms sharing electrons, usually between non-metals.
Chemical reactions rearrange atoms to form new substances. There are five main types of reactions: Combination , Decomposition , Single Replacement , Double Replacement , and Combustion (hydrocarbons reacting with oxygen to form CO₂ and H₂O).
Test Tip: When identifying reaction types, look at the pattern of reactants and products. For example, if two substances combine to make one product, it's a combination reaction!
Chemical Reactions and Stoichiometry
Chemical reactions can be either irreversible (reactants convert completely to products) or reversible (reaching equilibrium with both reactants and products present). The energy changes in reactions matter too—endothermic reactions absorb heat while exothermic reactions release heat.
When calculating quantities in chemical reactions, the mole concept is your best friend. One mole equals 6.02 × 10²³ particles (Avogadro's number). The molar mass tells you the mass of one mole of a substance in grams.
In most reactions, we need to identify the limiting reactant—the reactant that gets used up first and controls how much product forms. Any other reactants are considered excess reactants. Finding the limiting reactant helps us calculate the maximum amount of product possible from a given set of reactants.
Quick Tip: When solving stoichiometry problems, convert everything to moles first, then use the balanced equation to find relationships, and finally convert to the units requested in the problem.
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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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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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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
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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
Atomic Theory and Bonding: Key Notes and Reactions
Atomic theory is the foundation of modern chemistry, explaining how matter is structured at its most basic level. Understanding atomic models, chemical bonding, and reactions helps us make sense of how elements interact to form the world around us.
Evolution of Atomic Models
The way we understand atoms has changed dramatically over time. It all started with Democritus's Spherical Model, which imagined atoms as tiny, indivisible spheres. John Dalton expanded this by stating atoms are neither created nor destroyed during chemical reactions.
As technology advanced, so did our understanding. Thomson's Plum Pudding Model suggested atoms were positive spheres with negative electrons embedded throughout. This was overturned by Rutherford's Nuclear Model, which discovered that atoms have a concentrated, positive nucleus with mostly empty space around it.
Bohr's Planetary Model represented a major breakthrough, proposing that electrons orbit the nucleus in specific energy levels, similar to planets orbiting the sun. Finally, the Quantum Mechanical Model by Schrödinger revolutionized our understanding by describing electrons as waves with probabilistic locations rather than definite particles.
Remember This! Atomic theory explains important laws like Conservation of Mass (matter cannot be created or destroyed) and Definite Composition (elements combine in predictable ratios to form compounds).
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Quantum Theory and the Periodic Table
Quantum theory helped explain mysteries that previous atomic models couldn't. Einstein showed that light behaves as particles called photons, while de Broglie demonstrated that matter can behave like waves—a concept called wave-particle duality.
The location and behavior of electrons is described by four quantum numbers: principal (n), angular momentum (l), magnetic (mₗ), and spin (mₛ). These numbers follow important rules like Pauli's Exclusion Principle (no two electrons can have identical quantum numbers) and Hund's Rule (electrons occupy orbitals singly before pairing up).
The periodic table organizes elements based on their properties and electron arrangements. Elements are arranged in groups (vertical columns) and periods (horizontal rows). Groups share similar chemical properties because they have the same number of valence electrons. For example, Group IA elements (alkali metals) all have one valence electron and are highly reactive, while Group VIIIA (noble gases) have full outer shells and rarely react.
Fun Fact: Dmitri Mendeleev created the first widely accepted periodic table in 1869, leaving gaps for elements that hadn't been discovered yet. His predictions about these unknown elements turned out to be amazingly accurate!
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Periodic Trends and Chemical Bonds
Elements show predictable patterns across the periodic table. Atomic radius generally decreases across a period and increases down a group. Electronegativity (how strongly atoms attract electrons) increases across a period and decreases down a group, which helps predict how elements will bond.
When atoms interact, they form chemical bonds. Ionic bonds occur when electrons transfer completely between atoms, typically from a metal to a non-metal, creating charged ions that attract each other. Covalent bonds involve atoms sharing electrons, usually between non-metals.
Chemical reactions rearrange atoms to form new substances. There are five main types of reactions: Combination , Decomposition , Single Replacement , Double Replacement , and Combustion (hydrocarbons reacting with oxygen to form CO₂ and H₂O).
Test Tip: When identifying reaction types, look at the pattern of reactants and products. For example, if two substances combine to make one product, it's a combination reaction!
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Chemical Reactions and Stoichiometry
Chemical reactions can be either irreversible (reactants convert completely to products) or reversible (reaching equilibrium with both reactants and products present). The energy changes in reactions matter too—endothermic reactions absorb heat while exothermic reactions release heat.
When calculating quantities in chemical reactions, the mole concept is your best friend. One mole equals 6.02 × 10²³ particles (Avogadro's number). The molar mass tells you the mass of one mole of a substance in grams.
In most reactions, we need to identify the limiting reactant—the reactant that gets used up first and controls how much product forms. Any other reactants are considered excess reactants. Finding the limiting reactant helps us calculate the maximum amount of product possible from a given set of reactants.
Quick Tip: When solving stoichiometry problems, convert everything to moles first, then use the balanced equation to find relationships, and finally convert to the units requested in the problem.
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