Rules of Electron Configuration
Learn how electrons fill atomic orbitals with interactive demonstrations of the Aufbau principle, Pauli exclusion principle, and Hund's rule.
About this simulation
- What
- An interactive Chemistry simulation of Rules of Electron Configuration.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-06-11
Key Concepts
Aufbau Principle
Electrons always fill atomic orbitals of the lowest available energy levels first. Follows energy level crossover rules (e.g., 4s fills before 3d).
Pauli Exclusion Principle
No two electrons in an atom can have the same four quantum numbers, meaning a single orbital can hold a maximum of two electrons with opposite spins.
Hund's Rule
For degenerate orbitals (like the three 2p orbitals), electrons will singly occupy empty orbitals with parallel spins to maximize exchange energy and stability.
Exceptional Configurations
Transition metals (like Chromium and Copper) undergo electron shifts from the 4s to the 3d subshell to achieve extra stability through half-filled (3d⁵) or fully-filled (3d¹⁰) states.
Interactive Electron Configuration
The ground-state electron configuration of an atom is precisely determined by three fundamental quantum mechanical rules. Understanding these rules allows us to derive the configuration of any element, explaining chemical periodicity and reactivity.
Use this interactive visualizer to explore how the Aufbau Principle determines energy ordering, how the Pauli Exclusion Principle enforces spin pairing, and how Hund's Rule maximizes exchange energy.
Select an element from the Configuration Builder to watch the step-by-step orbital filling process and identify special transition metal exceptions.
Common Questions
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