Electron Configuration Calculator

About the Electron Configuration Calculator

An electron configuration describes how electrons are distributed among the atomic orbitals of an atom. Electrons fill orbitals in order of increasing energy according to the aufbau principle, with each orbital holding at most two electrons (Pauli exclusion principle), and degenerate orbitals being half-filled before any is fully occupied (Hund's rule).

Electron configurations directly determine an element's chemical properties: its position in the periodic table, ionization energy, electron affinity, bonding behavior, and magnetic properties. The configuration also reveals how many valence electrons are available for bonding and whether any are unpaired.

This calculator generates the electron configuration for any element, with options for atomic number, symbol, or ion. It shows the full configuration, noble gas shorthand, orbital box diagrams with electron arrows, valence electron count, and the set of quantum numbers for the last electron added. Common exceptions (Cr, Cu, and others) are handled correctly.

When This Page Helps

Quickly generate correct electron configurations including exceptions. View orbital diagrams, identify unpaired electrons, and determine magnetic properties for any element or ion.

How to Use the Inputs

1. Enter an element symbol, name, or atomic number.
2. Optionally specify an ion charge (e.g., +2 for Fe²⁺).
3. View the full electron configuration and noble gas shorthand.
4. Examine the orbital diagram with up/down arrows.
5. Check valence electrons and quantum numbers.
6. Click element presets for quick examples.
7. Compare configurations of similar elements in the table.

Example Calculation

Tips & Best Practices

• Remember: when making cations from transition metals, remove s electrons before d electrons.
• The number of unpaired electrons determines magnetic moment: μ = √(n(n+2)) Bohr magnetons.
• Noble gas core notation uses [He], [Ne], [Ar], [Kr], [Xe], or [Rn] as the starting point.
• Period number = highest occupied principal quantum number for that element.
• Group number (1-8 or 1-18) relates directly to the number of valence electrons.
• Isoelectronic species have the same electron configuration: Na⁺, Ne, F⁻ are all 1s² 2s² 2p⁶.

The Quantum Mechanical Model

Each electron in an atom is described by four quantum numbers: n (1,2,3...), l (0 to n-1), mₗ (-l to +l), and mₛ (+½ or -½). No two electrons can share all four quantum numbers (Pauli exclusion). The aufbau principle and Hund's rule govern the order of filling.

Anomalous Configurations

Several elements prefer half-filled or fully filled d and f subshells. Chromium ([Ar] 4s¹ 3d⁵) and copper ([Ar] 4s¹ 3d¹⁰) are the most commonly tested examples. In the f-block, anomalies are even more common because the energy differences between 4f, 5d, and 6s orbitals are very small.

Configurations and Chemical Properties

Electron configurations explain periodic trends: elements in the same group share the same valence configuration (e.g., all alkali metals are [noble gas] ns¹). Ionization energies, electron affinities, and electronegativity all correlate with how tightly the outermost electrons are held.

Frequently Asked Questions

• Why does chromium have [Ar] 4s¹ 3d⁵ instead of 4s² 3d⁴?

  Half-filled subshells (d⁵) are extra stable due to exchange energy. Chromium promotes one 4s electron to achieve this favored configuration, and copper does similarly to get a full d¹⁰.

• How do electron configurations work for ions?

  For cations, remove electrons from the highest principal quantum number first (usually s before d). For Fe²⁺, remove two 4s electrons: [Ar] 3d⁶. For anions, add electrons to the next available orbital.

• What are valence electrons?

  Electrons in the outermost shell (highest n). Main group: s and p in outer shell. Transition metals: typically count only s electrons as valence, or both s and d for bonding.

• What do the quantum numbers represent?

  n = principal (shell), l = angular momentum (subshell shape: 0=s, 1=p, 2=d, 3=f), mₗ = magnetic (orbital orientation), mₛ = spin (+½ or -½). This keeps planning practical and lowers the chance of preventable errors.

• Why is the aufbau order not simply 1s, 2s, 2p, 3s, 3p, 3d?

  Due to electron-electron repulsion and shielding effects, 4s fills before 3d because its greater penetration near the nucleus gives it lower energy in multi-electron atoms. This keeps planning practical and lowers the chance of preventable errors.

• How many elements have anomalous configurations?

  About 20 elements have configurations that differ from strict aufbau predictions, mostly in the d-block (Cr, Cu, Mo, Ag, Au, Pt) and f-block (many lanthanides and actinides). This keeps planning practical and lowers the chance of preventable errors.