All calculatorsElectron Configuration Calculator
Get the full and condensed electron configuration for any element or ion. Handles aufbau filling, Hund’s rule, Pauli exclusion, and common exceptions (Cr, Cu, Mo, Ag, Au, Pd, Pt, etc.). Includes a step-by-step filling trace and an optional mini chart of electrons per shell.
Background
Electron configurations describe how electrons occupy atomic orbitals. We fill orbitals by increasing energy (aufbau), maximize parallel spins in degenerate orbitals (Hund), and obey the Pauli exclusion principle. Transition-metal ions typically lose ns electrons before (n−1)d.
How to use this calculator
- Input: Type symbol (Fe), name (Iron), or atomic number (26). Add a charge for ions (e.g., 2 for 2⁺).
- Output: Full and condensed configurations, step-by-step orbital filling, and an optional per-shell chart.
- Ions: For cations, electrons are removed from the highest n; in transition metals, ns are removed before (n−1)d.
- Exceptions: Common cases (Cr, Cu, Mo, Ag, Au, Pd, Pt, etc.) are handled with known experimental configurations.
Formula & Equation Used
Aufbau order (through n=7): 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Subshell capacities: s=2, p=6, d=10, f=14.
Condensed form: Replace filled core with nearest preceding noble gas: e.g., [Ar] 4s² 3d⁶.
Ionization rule (simplified): Remove from highest n; for transition metals, remove ns before (n−1)d.
Example Problems & Step-by-Step Solutions
Example 1 — Fe (Z=26)
Fe → [Ar] 4s² 3d⁶. For Fe²⁺, remove 4s electrons first: [Ar] 3d⁶.
Example 2 — Cu (exception)
Cu → [Ar] 3d¹⁰ 4s¹ (not 3d⁹ 4s²). Cu⁺ → [Ar] 3d¹⁰.
Example 3 — O²⁻
O: 1s² 2s² 2p⁴; O²⁻ adds two e⁻ → 1s² 2s² 2p⁶ = [He] 2s² 2p⁶ = [Ne].
Frequently Asked Questions
Q: Why do some elements have “exceptions”?
Electron–electron interactions and small energy differences can favor half-filled or filled subshells (e.g., d⁵ or d¹⁰), producing observed deviations.
Q: How are electrons removed for transition-metal cations?
From the valence shell first (highest n), specifically removing ns before (n−1)d.
Q: Is the aufbau order always exact?
It’s a powerful guideline for ground-state atoms/ions, but subtle variations exist—our calculator applies standard undergraduate rules plus common exceptions.
