Periodic Trends Summary
Trends in radius, ionization energy and electronegativity follow nuclear charge and shielding.
About this topic
Across a period, nuclear charge increases while shielding remains similar, so atomic radius decreases while ionisation energy and electronegativity increase. Down a group, extra shells increase size and shielding, so radius increases while ionisation energy and electronegativity decrease. Metallic character is the reverse of ionisation energy.
A handy mental picture is a diagonal arrow from the bottom left to the top right of the table: toward the top right, atoms are smaller, hold electrons tighter and attract bonding electrons strongly, with fluorine as the extreme. Toward the bottom left, atoms are larger, lose electrons readily and are the most metallic, with francium and caesium as the extremes. Reactivity splits: for metals it rises down a group, but for non-metals such as halogens it rises up a group.
Use trends to compare. Which is larger, magnesium or sulfur? Both are in period 3, magnesium is to the left, so it is larger. Which has the higher ionisation energy, oxygen or sulfur? Oxygen, because it is higher up. Trends help predict bond type and compound properties for elements you have never studied.
Beware of exceptions, such as the dips in ionisation energy, and remember that noble gases are left out of electronegativity trends.
Key ideas
- Across a period: more protons, smaller radius
- Down a group: more shells, bigger radius
- Metallic character grows down
Quick check
Use cases: where Periodic Trends Summary helps
- Homework: review the key idea behind Periodic Trends Summary before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Periodic Trends Summary without notes.
- Visual learning: play with the interactive lab to see how Periodic Trends Summary changes when you adjust its inputs.
- Teaching a friend: explain Periodic Trends Summary in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Periodic Trends Summary?
Trends in radius, ionization energy and electronegativity follow nuclear charge and shielding.
What will I learn in Periodic Trends Summary?
Across a period: more protons, smaller radius. Down a group: more shells, bigger radius. Metallic character grows down.
Is Periodic Trends Summary part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Periodic Trends Summary lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Periodic Trends Summary?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.