What Is Electron Configuration?
Electron configuration describes how electrons are distributed among the orbitals of an atom. It follows a set of rules — the Aufbau principle, Pauli exclusion principle, and Hund's rule — to determine the order in which electrons fill available energy levels.
Understanding electron configuration is essential for predicting chemical behavior, bonding patterns, and the physical properties of elements. This tool lets you instantly look up the configuration for any of the 118 elements in the periodic table.
Key Concepts
Subshells (s, p, d, f)
Noble Gas Notation
Configuration Exceptions
Quantum Numbers
How to Use
Select an Element
Choose your element using one of three convenient methods:
- Click the periodic table — Click any cell to select that element instantly
- Search — Type a name (e.g., "Iron"), symbol ("Fe"), or atomic number ("26") in the search bar
- Arrow keys — Press the left/right arrow keys or the navigation buttons to step through elements
Read the Results
Once an element is selected, you will see comprehensive information:
- Full configuration — The complete electron configuration written out subshell by subshell (e.g., 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ for Iron)
- Noble gas notation — The abbreviated form using a noble gas core (e.g., [Ar] 4s² 3d⁶)
- Valence electrons — The number of electrons in the outermost shell
- Unpaired electrons — How many electrons are not paired in orbitals
- Block — Whether the element belongs to the s, p, d, or f block
- Quantum numbers — The four quantum numbers of the last electron added
View Ion Configurations
Use the charge selector next to the element name to switch between neutral atoms and ions. For example, selecting Fe²⁺ shows the configuration after removing two electrons — which are taken from the 4s subshell before 3d, following the standard removal rules for transition metals.
Explore the Orbital Diagram
The orbital diagram section shows each subshell as a series of boxes. Arrows represent electrons: an up arrow for spin-up (+½) and a down arrow for spin-down (-½). The filling follows Hund's rule — each orbital gets one electron before any orbital gets a second.
Features
Complete Periodic Table
An interactive periodic table covering all 118 elements, color-coded by category for easy identification.
- Nonmetals, noble gases, alkali metals
- Alkaline earth metals, transition metals
- Post-transition metals, metalloids
- Lanthanides and actinides
Full and Shorthand Notation
View the complete electron configuration written subshell by subshell, as well as the noble gas notation.
- Color-coded subshells: s (blue), p (amber)
- d (purple), f (green) for quick visual parsing
- Noble gas core symbols like [Ar] or [Xe]
Exception Handling
Twenty elements have configurations that deviate from the standard Aufbau filling order.
- Clearly marked with "Exception" badge
- Hover to reveal stability reasons
- Half-filled or fully filled d and f subshells
Ion Configuration
Switch between neutral atoms and charged ions using the charge selector.
- Correct electron removal rules applied
- Transition metals: 4s removed before 3d
- Matches real chemical behavior
Orbital Diagram
A visual box diagram shows how electrons fill orbitals following Hund's rule.
- Each box represents one orbital
- Up and down arrows indicate electron spin
- Shows full, half-filled, or empty orbitals
Quantum Numbers
Displays the four quantum numbers (n, l, ml, ms) of the last electron added.
- Principal quantum number (n)
- Azimuthal quantum number (l)
- Magnetic and spin quantum numbers
Frequently Asked Questions
Why do some elements have "Exception" configurations?
Certain elements like Chromium (Cr) and Copper (Cu) have configurations that differ from what the Aufbau principle predicts. This happens because half-filled or fully filled d and f subshells are exceptionally stable.
Why are electrons removed from 4s before 3d in transition metal ions?
Although 4s fills before 3d in neutral atoms, when forming cations, 4s electrons are removed first. This is because in a positively charged ion, the 3d orbitals drop to a lower energy than 4s due to reduced electron-electron repulsion.
Filling Order
- 4s fills before 3d
- Example: Fe = [Ar] 4s² 3d⁶
Removal Order
- 4s removed before 3d
- Example: Fe²⁺ = [Ar] 3d⁶
This tool correctly handles this removal order for all transition metal ions.
What do the quantum numbers mean?
The four quantum numbers describe the state of an electron in an atom:
n (Principal)
l (Azimuthal)
ml (Magnetic)
ms (Spin)
What is noble gas notation?
Noble gas notation is a shorthand for writing electron configurations. Instead of writing out all inner electrons, you replace them with the symbol of the nearest noble gas in brackets.
[Ne] 3s¹ because the first 10 electrons match Neon's configuration.This notation simplifies writing and reading configurations, especially for heavier elements with many electrons. It emphasizes the valence electrons that participate in chemical bonding.
How are valence electrons counted?
The method for counting valence electrons depends on the element type:
- Main group elements — Valence electrons are those in the highest principal energy level (outermost shell)
- Transition metals — Both the outermost s electrons and the (n-1)d electrons are counted as valence electrons, since d electrons participate in bonding
No comments yet. Be the first to comment!