Electron Configuration Visualizer
Select an element to see its full electron configuration, noble gas shorthand, and orbital filling diagram.
Select an element from the periodic table
What is electron configuration?
Electron configuration describes the arrangement of electrons in an atom's orbitals. Each element has a unique configuration that determines its chemical properties, bonding behavior, and position in the periodic table. The configuration follows specific rules about how electrons fill available energy levels, with lower-energy orbitals filling first.
The notation uses subshell labels (1s, 2s, 2p, 3s, 3p, 3d, etc.) with superscript numbers indicating how many electrons occupy each subshell. For example, oxygen (8 electrons) has the configuration 1s2 2s2 2p4. This tells us oxygen has 2 electrons in the 1s orbital, 2 in the 2s, and 4 in the 2p subshell.
Rules for filling orbitals
- Aufbau principle: Electrons fill the lowest-energy orbitals first. The filling order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, and so on.
- Pauli exclusion principle: Each orbital holds at most 2 electrons, and they must have opposite spins.
- Hund's rule: When filling orbitals of equal energy, electrons spread out with parallel spins before pairing up.
How to use this tool
Select an element by name, symbol, or atomic number. The tool displays the full electron configuration, the abbreviated noble gas notation, an orbital diagram showing electron spin, and the number of valence electrons. It also highlights exceptions to the standard filling order (like chromium and copper).
Noble gas notation
For elements beyond helium, the configuration can be abbreviated by replacing the inner electrons with the symbol of the preceding noble gas in brackets. Iron's full configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d6, which abbreviates to [Ar] 4s2 3d6. This notation makes it easier to see the valence (outer) electrons that participate in bonding.
Frequently asked questions
Why do some elements not follow the expected filling order?
Elements like chromium ([Ar] 3d5 4s1 instead of 3d4 4s2) and copper ([Ar] 3d10 4s1 instead of 3d9 4s2) have exceptions because a half-filled or fully-filled d subshell provides extra stability. The energy differences between the 4s and 3d orbitals are small enough that this stability bonus overrides the normal filling order.
What are valence electrons and why do they matter?
Valence electrons are the outermost electrons that participate in chemical bonding. They determine an element's reactivity, the types of bonds it forms, and its position in the periodic table. Elements in the same group (column) have the same number of valence electrons, which is why they have similar chemical properties.