The periodic table organizes elements based on their properties, with... Show more
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Dec 22, 2025
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Periodic Table Trends and Properties Explained
Gabriella Mulé
@bellamule08
1 / 4
Development and Periodic Trends
The periodic table we use today stems from the work of scientists like Dmitri Mendeleev and Lothar Meyer. Mendeleev was so confident in the periodic patterns that he accurately predicted properties of undiscovered elements like germanium .
When examining the table, we see consistent patterns in properties like atomic size, ionization energy, and electron affinity. These trends are largely explained by effective nuclear charge (Zeff), which is the actual charge an electron experiences after accounting for shielding by other electrons. We calculate it using the formula: Zeff = Z - S, where Z is the atomic number and S is the screening constant.
Atomic size generally decreases as you move right across a period due to increasing effective nuclear charge pulling electrons closer to the nucleus. Conversely, atomic size increases as you move down a group because electrons occupy higher energy levels farther from the nucleus.
Quick Tip: Remember that cations (positive ions) are always smaller than their parent atoms because removing electrons reduces repulsion, while anions (negative ions) are larger than their parent atoms because adding electrons increases repulsion.
In an isoelectric series (ions with the same number of electrons), size decreases with increasing nuclear charge as the same number of electrons are pulled closer to nuclei with more protons.
Ionization Energy and Electron Affinity
Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy refers to removing the first electron, the second ionization energy refers to removing the second electron, and so on. It always takes more energy to remove each successive electron, with a huge jump after all valence electrons are removed.
As you move down a group, ionization energy decreases because valence electrons are farther from the nucleus. As you move across a period, ionization energy generally increases as effective nuclear charge increases, but there are two notable exceptions:
- Between Groups IIA and IIIA (when switching from s to p orbitals)
- Between Groups VA and VIA (when removing an electron from a doubly occupied orbital)
Electron affinity measures the energy change when a gaseous atom gains an electron. More negative values indicate more energy released (more favorable). Like ionization energy, electron affinity generally becomes more negative (more favorable) moving left to right across a period, with similar exceptions.
Remember This: When learning about periodic trends, visualize electrons being pulled by the nucleus like gravity. More protons mean stronger pull, but distance and other electron repulsions weaken this effect.
Metals vs. Nonmetals
Metals dominate the left side of the periodic table and have distinctive properties. They're shiny, malleable, ductile, and excellent conductors of heat and electricity. In chemical reactions, metals tend to lose electrons to form positive ions (cations). Metal oxides typically form basic solutions when dissolved in water.
Nonmetals, found on the right side of the table, have nearly opposite properties. They're typically dull, brittle, and poor conductors. Nonmetals tend to gain electrons in reactions, forming negative ions (anions). Their oxides usually form acidic solutions when dissolved in water.
Between metals and nonmetals are the metalloids, which show mixed properties. Silicon, for example, looks shiny like a metal but is brittle and a relatively poor conductor like nonmetals.
Chemical Connection: Think about how these properties affect everyday materials. The copper in electrical wires is malleable and conductive (metal properties), while the carbon in pencil "lead" is brittle and non-conductive (nonmetal properties).
The alkali metals (Group 1) are extremely reactive metals with low melting points and densities. They react vigorously with water—some violently enough to catch fire! Similarly, the alkaline earth metals (Group 2) are reactive, though not quite as dramatic as their Group 1 neighbors. Their reactivity increases as you move down the group.
Important Element Families
Oxygen exists in two allotropes (forms of the same element): O₂ (the oxygen we breathe) and O₃ (ozone). It can form three different anions: oxide (O²⁻), peroxide (O₂²⁻), and superoxide (O₂¹⁻), each with different properties and applications.
Sulfur, another Group 16 element, is a weaker oxidizing agent than oxygen. Its most stable form is S₈, a ring-shaped molecule. This explains sulfur's distinctive yellow, crystalline appearance in its elemental state.
The halogens (Group 17) are classic nonmetals with large negative electron affinities, making them powerful oxidizing agents. They readily react with metals to form salts called halides. Chlorine's strong oxidizing properties make it useful as a water disinfectant.
Noble gases (Group 18) stand apart with their extremely high ionization energies and positive electron affinities. These properties make them almost completely unreactive—they exist as isolated atoms rather than molecules. Their stability comes from having completely filled outer electron shells.
Fun Fact: While noble gases were once thought to be completely inert, scientists have successfully created compounds with xenon, krypton, and even argon under extreme conditions!
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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
Periodic Table Trends and Properties Explained
Gabriella Mulé
@bellamule08
The periodic table organizes elements based on their properties, with elements in the same group having similar chemical behaviors. This arrangement reveals patterns in atomic properties that help us understand how elements interact with each other. Understanding these trends is... Show more
Development and Periodic Trends
The periodic table we use today stems from the work of scientists like Dmitri Mendeleev and Lothar Meyer. Mendeleev was so confident in the periodic patterns that he accurately predicted properties of undiscovered elements like germanium .
When examining the table, we see consistent patterns in properties like atomic size, ionization energy, and electron affinity. These trends are largely explained by effective nuclear charge (Zeff), which is the actual charge an electron experiences after accounting for shielding by other electrons. We calculate it using the formula: Zeff = Z - S, where Z is the atomic number and S is the screening constant.
Atomic size generally decreases as you move right across a period due to increasing effective nuclear charge pulling electrons closer to the nucleus. Conversely, atomic size increases as you move down a group because electrons occupy higher energy levels farther from the nucleus.
Quick Tip: Remember that cations (positive ions) are always smaller than their parent atoms because removing electrons reduces repulsion, while anions (negative ions) are larger than their parent atoms because adding electrons increases repulsion.
In an isoelectric series (ions with the same number of electrons), size decreases with increasing nuclear charge as the same number of electrons are pulled closer to nuclei with more protons.
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Ionization Energy and Electron Affinity
Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy refers to removing the first electron, the second ionization energy refers to removing the second electron, and so on. It always takes more energy to remove each successive electron, with a huge jump after all valence electrons are removed.
As you move down a group, ionization energy decreases because valence electrons are farther from the nucleus. As you move across a period, ionization energy generally increases as effective nuclear charge increases, but there are two notable exceptions:
- Between Groups IIA and IIIA (when switching from s to p orbitals)
- Between Groups VA and VIA (when removing an electron from a doubly occupied orbital)
Electron affinity measures the energy change when a gaseous atom gains an electron. More negative values indicate more energy released (more favorable). Like ionization energy, electron affinity generally becomes more negative (more favorable) moving left to right across a period, with similar exceptions.
Remember This: When learning about periodic trends, visualize electrons being pulled by the nucleus like gravity. More protons mean stronger pull, but distance and other electron repulsions weaken this effect.
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Metals vs. Nonmetals
Metals dominate the left side of the periodic table and have distinctive properties. They're shiny, malleable, ductile, and excellent conductors of heat and electricity. In chemical reactions, metals tend to lose electrons to form positive ions (cations). Metal oxides typically form basic solutions when dissolved in water.
Nonmetals, found on the right side of the table, have nearly opposite properties. They're typically dull, brittle, and poor conductors. Nonmetals tend to gain electrons in reactions, forming negative ions (anions). Their oxides usually form acidic solutions when dissolved in water.
Between metals and nonmetals are the metalloids, which show mixed properties. Silicon, for example, looks shiny like a metal but is brittle and a relatively poor conductor like nonmetals.
Chemical Connection: Think about how these properties affect everyday materials. The copper in electrical wires is malleable and conductive (metal properties), while the carbon in pencil "lead" is brittle and non-conductive (nonmetal properties).
The alkali metals (Group 1) are extremely reactive metals with low melting points and densities. They react vigorously with water—some violently enough to catch fire! Similarly, the alkaline earth metals (Group 2) are reactive, though not quite as dramatic as their Group 1 neighbors. Their reactivity increases as you move down the group.
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Important Element Families
Oxygen exists in two allotropes (forms of the same element): O₂ (the oxygen we breathe) and O₃ (ozone). It can form three different anions: oxide (O²⁻), peroxide (O₂²⁻), and superoxide (O₂¹⁻), each with different properties and applications.
Sulfur, another Group 16 element, is a weaker oxidizing agent than oxygen. Its most stable form is S₈, a ring-shaped molecule. This explains sulfur's distinctive yellow, crystalline appearance in its elemental state.
The halogens (Group 17) are classic nonmetals with large negative electron affinities, making them powerful oxidizing agents. They readily react with metals to form salts called halides. Chlorine's strong oxidizing properties make it useful as a water disinfectant.
Noble gases (Group 18) stand apart with their extremely high ionization energies and positive electron affinities. These properties make them almost completely unreactive—they exist as isolated atoms rather than molecules. Their stability comes from having completely filled outer electron shells.
Fun Fact: While noble gases were once thought to be completely inert, scientists have successfully created compounds with xenon, krypton, and even argon under extreme conditions!
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