Electron Configuration
Electron configuration lists where electrons live in orbitals.
About this topic
Electron configuration describes how electrons are distributed in subshells: s, p, d and f. They fill according to the Aufbau principle (lowest energy first), the Pauli exclusion principle (maximum two electrons per orbital with opposite spins) and Hund's rule (fill degenerate orbitals singly before pairing).
The subshells hold 2 (s), 6 (p), 10 (d) and 14 (f) electrons. The filling order follows 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on, which you can remember with a diagonal diagram. Notation shows the subshell followed by the number of electrons as a superscript. Oxygen, with 8 electrons, is 1s2 2s2 2p4. A shorthand uses the previous noble gas in brackets, so sodium is [Ne] 3s1.
Worked example: iron with 26 electrons is [Ar] 4s2 3d6. Because 4s fills before 3d, transition metals lose their 4s electrons first when forming ions. Chromium and copper are exceptions that favour half-filled or filled d subshells, giving [Ar] 4s1 3d5 and [Ar] 4s1 3d10.
Configurations explain the shape of the periodic table: the block an element sits in matches its last-filled subshell. They also explain magnetism and colour in compounds. Students often forget that 4s comes before 3d in filling, and should check that the superscripts add up to the atomic number.
Key ideas
- 1s, 2s, 2p, 3s …
- Aufbau, Pauli and Hund's rules
- Shorthand uses noble gas cores
Quick check
Use cases: where Electron Configuration helps
- Homework: review the key idea behind Electron Configuration before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Electron Configuration without notes.
- Visual learning: play with the interactive lab to see how Electron Configuration changes when you adjust its inputs.
- Teaching a friend: explain Electron Configuration 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 Electron Configuration?
Electron configuration lists where electrons live in orbitals.
What will I learn in Electron Configuration?
1s, 2s, 2p, 3s …. Aufbau, Pauli and Hund's rules. Shorthand uses noble gas cores.
Is Electron Configuration 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 Electron Configuration 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 Electron Configuration?
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.