Use our ground state configuration calculator for quick and accurate calculations. Free online tool.
The Aufbau principle provides the filling order for atomic orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. Each s-subshell holds up to 2 electrons, each p-subshell up to 6, each d-subshell up to 10, and each f-subshell up to 14. Using this sequence, the ground state configuration of carbon (Z=6) is 1s²2s²2p², and that of iron (Z=26) is [Ar]3d⁶4s². These configurations directly reflect how electrons populate available quantum states at minimal energy cost.
Notable exceptions to the straightforward Aufbau filling order occur in certain transition metals and lanthanides. For instance, chromium (Z=24) adopts [Ar]3d⁵4s¹ rather than [Ar]3d⁴4s², because a half-filled d-subshell offers extra exchange-energy stability. Similarly, copper (Z=29) is [Ar]3d¹⁰4s¹ instead of [Ar]3d⁹4s². These anomalies arise from quantum mechanical effects that make certain configurations energetically favourable beyond simple orbital ordering.
Ground state configurations are the starting point for predicting an element's chemical behaviour: oxidation states, magnetic properties, spectroscopic transitions, and bonding tendencies all flow directly from this foundational description. Our ground state configuration calculator applies the Aufbau principle with known exceptions to produce the correct noble-gas notation for any element from hydrogen (Z=1) to oganesson (Z=118). You can use the result to determine the number of unpaired electrons (and hence paramagnetism), identify valence electrons, or write electron-dot diagrams with confidence.
Electron configuration, orbital diagrams, valence electrons, and electron arrangement
Explore CategoryThe ground state electron configuration is the lowest-energy arrangement of an atom's electrons across its atomic orbitals. It is the most stable configuration and the reference state from which excited states are defined.
The three rules are the Aufbau principle (fill orbitals from lowest to highest energy), the Pauli exclusion principle (each orbital holds at most two electrons with opposite spins), and Hund's rule (electrons occupy degenerate orbitals singly before any orbital receives a second electron).
Chromium (Z=24) adopts [Ar]3d⁵4s¹ and copper (Z=29) adopts [Ar]3d¹⁰4s¹ because half-filled and fully filled d-subshells have extra exchange-energy stability that makes these configurations lower in energy than the configurations predicted by simple Aufbau filling.
Noble-gas notation abbreviates the filled inner-shell configuration by enclosing the symbol of the preceding noble gas in brackets. For example, sodium's full configuration is 1s²2s²2p⁶3s¹, written as [Ne]3s¹ using noble-gas notation, which highlights only the valence electrons.
An atom is paramagnetic (attracted to magnetic fields) if it has one or more unpaired electrons, and diamagnetic if all electrons are paired. By reading the ground state configuration and counting unpaired electrons in each subshell, you can determine whether a substance is paramagnetic or diamagnetic.