Skip to main content

Electron Configuration Calculator

Ready to calculate
Aufbau · Pauli · Hund.
92 Elements (H → U).
Orbital Diagram + Anomalies.
100% Free.
No Data Stored.

How it Works

01Pick the Element

92 elements supported — Hydrogen (Z=1) through Uranium (Z=92)

02Apply Aufbau Order

Fill orbitals lowest-energy first: 1s → 2s → 2p → 3s → 3p → 4s → 3d → ...

03Apply Hund's Rule

Within a subshell, fill each orbital singly with parallel spins before pairing

04Get Full Output

Configuration · noble-gas shorthand · orbital diagram · block · group · anomalies

What is an Electron Configuration Calculator?

An electron configuration is the complete map of where every electron in an atom lives — which energy level (n), which subshell (s, p, d, or f), and within that subshell which orbital. It's the foundation of all chemistry: configurations dictate which elements bond to which, which exist as gases at room temperature, which conduct electricity, which are colored, and why the periodic table has the shape it does. Our Electron Configuration Calculator looks up the ground-state configuration of any element from Hydrogen (Z=1) through Uranium (Z=92) and presents it in three forms: the full subshell-by-subshell breakdown, the noble-gas shorthand, and a visual orbital filling diagram showing how electrons distribute (Hund's rule + Pauli exclusion).

Pick the element from the alphabetical dropdown — 92 elements available — and the calculator returns the configuration plus the electron's "address" in the periodic table: atomic number Z, total electron count, period, group, and block (s, p, d, or f). For elements with Aufbau anomalies — Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, Pt, Au, Gd, Th — the calculator displays the actual configuration (which deviates from the simple Aufbau prediction) along with a clear explanation of why (extra stability of half-filled or fully filled subshells).

Three rules govern ground-state electron configurations: Aufbau (fill lowest-energy orbitals first), Pauli exclusion (max 2 electrons per orbital, with opposite spins), and Hund's rule (fill orbitals within a subshell singly with parallel spins before pairing). The orbital filling diagram in the output shows all three rules in action — boxes for orbitals, up/down arrows for electron spins, color-coded by subshell type.

Pro Tip: Pair this with our Molar Mass Calculator for stoichiometry, or our Electronegativity Calculator for related bonding analysis.

How to Use the Electron Configuration Calculator?

Pick the Element: 92 elements supported (H through U). The dropdown shows each element by its full name, symbol, and atomic number Z. Default is Hydrogen.
Press Calculate: The tool looks up the curated ground-state configuration from a verified IUPAC table.
Read the Noble-Gas Shorthand: The compact form using the previous noble gas's configuration as a base — e.g., sodium is [Ne] 3s¹ rather than 1s² 2s² 2p⁶ 3s¹. Standard convention in college and graduate chemistry.
Read the Full Configuration: Every subshell explicitly listed with its electron count — useful for working out valence-electron counts and oxidation states.
Inspect the Orbital Diagram: Color-coded by subshell (s = rose, p = amber, d = blue, f = emerald), with electron arrows (↑ +½, ↓ −½) showing Hund's rule electron distribution within each subshell.

How do I work out the electron configuration?

Electron configurations follow three rules from quantum mechanics — Aufbau, Pauli exclusion, and Hund. Together they determine the unique ground-state configuration of every element. Here's the complete framework:

Think of orbitals like seats in a stadium with sections (subshells) and rows (energy levels). Aufbau says you fill the cheapest seats first. Pauli says no more than 2 fans per seat (and they must face opposite ways). Hund says you spread out before doubling up. Combined, these three rules give the complete seating chart for any atom.

Rule 1: Aufbau Principle

Electrons fill orbitals in order of increasing energy. The Madelung rule (n + l) gives the order:

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p

Note: 4s fills before 3d (because 4s has lower n+l), but once 3d starts filling, 4s and 3d energies become similar and can swap order in some elements (Cr, Cu anomalies).

Rule 2: Pauli Exclusion Principle

No two electrons in an atom can have the same four quantum numbers.

Practical consequence: max 2 electrons per orbital, and they must have opposite spins (one ↑, one ↓). This caps subshell capacities: s = 2 e⁻ (1 orbital), p = 6 e⁻ (3 orbitals), d = 10 e⁻ (5 orbitals), f = 14 e⁻ (7 orbitals).

Rule 3: Hund's Rule of Maximum Multiplicity

Within a subshell, electrons fill each orbital singly (with parallel spins) before any orbital gets a second electron.

Example: nitrogen's 2p³ is three single electrons in the three p orbitals (all spin-up), not two paired in one orbital + one alone. This minimizes electron-electron repulsion and maximizes total spin (lowest energy = ground state).

Aufbau Anomalies (Cr, Cu, Mo, Ag, Au, Pd, Pt, ...)

Some transition metals violate the simple Aufbau prediction because half-filled (d⁵) and fully filled (d¹⁰) subshells have extra exchange-energy stability:

  • Chromium (Z=24): [Ar] 3d⁵ 4s¹ not [Ar] 3d⁴ 4s² (half-filled 3d⁵)
  • Copper (Z=29): [Ar] 3d¹⁰ 4s¹ not [Ar] 3d⁹ 4s² (filled 3d¹⁰)
  • Molybdenum (Z=42): [Kr] 4d⁵ 5s¹ (same logic as Cr)
  • Silver (Z=47): [Kr] 4d¹⁰ 5s¹ (same logic as Cu)
  • Palladium (Z=46): [Kr] 4d¹⁰ (BOTH 5s electrons promoted — unique among transition metals)
  • Platinum (Z=78): [Xe] 4f¹⁴ 5d⁹ 6s¹
  • Gold (Z=79): [Xe] 4f¹⁴ 5d¹⁰ 6s¹
  • Gadolinium (Z=64): [Xe] 4f⁷ 5d¹ 6s² (half-filled 4f⁷)

Reading the Periodic Table

The periodic table is literally a map of electron configurations. Group 1 is s¹ (alkali metals), Group 2 is s² (alkaline earths), Groups 13–18 are p¹ through p⁶, transition metals (Groups 3–12) are d¹ through d¹⁰, lanthanides and actinides are f-block. Period number = highest occupied energy level (n). The block (s, p, d, f) tells you which subshell is being filled.

Real-World Example

Electron Configuration Calculator – Atoms In Practice

Consider iron (Fe, Z = 26) — the element responsible for hemoglobin's oxygen binding and structural steel:
  • Step 1: Iron has 26 electrons. Apply Aufbau order to fill 26 electrons.
  • Step 2: 1s² (2) + 2s² (4) + 2p⁶ (10) + 3s² (12) + 3p⁶ (18) — that's the argon core. Then 4s² (20) + 3d⁶ (26).
  • Step 3: Full configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Noble-gas shorthand: [Ar] 3d⁶ 4s².
  • Step 4: 3d⁶ filling: by Hund's rule, fill all 5 d orbitals singly first (5 spin-up electrons), then pair the 6th in the lowest. Result: 4 unpaired electrons in 3d. This explains why iron is paramagnetic and ferromagnetic.
  • Step 5: Periodic placement: d-block (transition metal), period 4, group 8. Standard Aufbau, no anomaly.

Now consider the famous chromium anomaly (Cr, Z = 24): simple Aufbau predicts [Ar] 3d⁴ 4s². But the actual ground state is [Ar] 3d⁵ 4s¹. Why? A half-filled 3d⁵ subshell (all 5 d orbitals singly occupied with parallel spins) has extra "exchange-energy" stability. The energy gain from completing the half-filled d outweighs the energy cost of leaving 4s singly occupied. Same logic explains Cu ([Ar] 3d¹⁰ 4s¹), Mo, Ag, Au — all have exceptional stability of d⁵ or d¹⁰ subshells.

For caesium (Cs, Z = 55): [Xe] 6s¹. Single 6s electron — explains why Cs is the most reactive stable alkali metal: that lone 6s electron is far from the nucleus and shielded by 54 inner electrons, so it ionizes easily (lowest first ionization energy of any stable element, ~3.9 eV).

Who Should Use the Electron Configuration Calculator?

1
Chemistry Students: Look up configurations for any element, understand periodic-table block placement, predict valence electrons and oxidation states.
2
General Chemistry Coursework: Solve homework problems on ionization energies, electron affinities, magnetism (paramagnetic vs diamagnetic), and chemical bonding patterns.
3
Organic & Inorganic Chemists: Predict reactivity from valence-shell occupations; rationalize transition-metal coordination geometries from d-orbital filling.
4
Materials Scientists: Magnetic and electronic properties depend on unpaired d/f electrons — Fe³⁺, Mn²⁺, Gd³⁺ are common in high-spin systems.
5
Spectroscopists: UV-Vis absorption, EPR, X-ray fluorescence — all depend on the electron configuration and the resulting term symbols.
6
Physics Students: Quantum mechanics applications — Slater determinants, term symbols, atomic spectra all start from the ground-state configuration.

Technical Reference

Quantum Numbers. Every electron is described by 4 quantum numbers: n (principal, energy level), l (azimuthal, subshell shape: 0=s, 1=p, 2=d, 3=f), mₗ (magnetic, orbital orientation: −l to +l), and mₛ (spin, ±½). Pauli exclusion: no two electrons share all four. Practical consequence: 2 electrons per orbital, opposite spins.

Subshell Capacities:

  • s subshell: 1 orbital × 2 electrons = 2 e⁻ max
  • p subshell: 3 orbitals × 2 = 6 e⁻ max
  • d subshell: 5 orbitals × 2 = 10 e⁻ max
  • f subshell: 7 orbitals × 2 = 14 e⁻ max

Madelung Rule (Aufbau Order). Subshells fill in order of increasing (n + l), with ties broken by lower n. Result:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Note that 4s (n+l = 4+0 = 4) fills before 3d (n+l = 3+2 = 5) despite higher n. After filling, the 4s electrons are actually higher in energy than 3d electrons — which is why 4s is the FIRST to ionize in transition-metal cations.

Cation Configurations. When a transition metal forms a cation, it loses outer-shell s electrons FIRST, then d electrons. So Fe ([Ar] 3d⁶ 4s²) → Fe²⁺ is [Ar] 3d⁶ (lost both 4s electrons), not [Ar] 3d⁴ 4s². For Fe³⁺: [Ar] 3d⁵ (lost both 4s + one 3d). This is why Fe³⁺ is high-spin with all 5 d electrons unpaired (half-filled stability).

The 19 Known Aufbau Anomalies (gas-phase ground state):

  • Cr (24): 3d⁵ 4s¹
  • Cu (29): 3d¹⁰ 4s¹
  • Nb (41): 4d⁴ 5s¹
  • Mo (42): 4d⁵ 5s¹
  • Ru (44): 4d⁷ 5s¹
  • Rh (45): 4d⁸ 5s¹
  • Pd (46): 4d¹⁰ (no 5s electrons!)
  • Ag (47): 4d¹⁰ 5s¹
  • La (57): 5d¹ 6s² (no 4f)
  • Ce (58): 4f¹ 5d¹ 6s²
  • Gd (64): 4f⁷ 5d¹ 6s²
  • Pt (78): 5d⁹ 6s¹
  • Au (79): 5d¹⁰ 6s¹
  • Ac (89): 6d¹ 7s² (no 5f)
  • Th (90): 6d² 7s² (no 5f)
  • Pa (91): 5f² 6d¹ 7s²
  • U (92): 5f³ 6d¹ 7s²
  • Np (93): 5f⁴ 6d¹ 7s²
  • Cm (96): 5f⁷ 6d¹ 7s²

Block Definitions. The block of an element is determined by which subshell is being filled. s-block = Groups 1, 2, plus He (filling ns). p-block = Groups 13–18 (filling np). d-block = Groups 3–12, transition metals (filling (n−1)d). f-block = lanthanides + actinides (filling (n−2)f). Period = highest occupied n.

Key Takeaways

The ground-state electron configuration is the most fundamental piece of information about any atom — it dictates valence, bonding, magnetism, color, reactivity, and periodic-table placement. The three rules (Aufbau, Pauli exclusion, Hund) cover 99% of cases; the 19 known anomalies (Cr, Cu, Mo, Ag, Au, Pd, Pt, Gd, Lu, ...) come from extra stability of half-filled and filled subshells. Use the ToolsACE Electron Configuration Calculator to look up the configuration for any element from H through U, get the noble-gas shorthand, the visual orbital filling diagram, and a clear explanation of any Aufbau anomaly. Bookmark it for general chemistry, inorganic chemistry, materials science, and spectroscopy work.

Frequently Asked Questions

What is the Electron Configuration Calculator?
An electron configuration is the complete inventory of where every electron in an atom lives — which energy level, which subshell (s, p, d, or f), and which orbital. Our calculator looks up the verified ground-state configuration for any element from Hydrogen (Z=1) through Uranium (Z=92) and returns it in three forms: noble-gas shorthand (e.g., Na = [Ne] 3s¹), full subshell-by-subshell, and visual orbital diagram showing electrons distributed by Hund's rule.

Includes period/group/block placement and explicit explanations of all 19 known Aufbau anomalies (Cr, Cu, Mo, Ag, Au, Pd, Pt, Gd, etc.) where extra stability of half-filled or filled subshells overrides the standard filling order. Designed for chemistry students, inorganic chemists, materials scientists, spectroscopists, and physics students — runs entirely in your browser.

Pro Tip: For more chemistry tools, try our Molar Mass Calculator.

What are the three rules for electron configurations?
1. Aufbau principle: Fill orbitals in order of increasing energy (1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → ...). Use the Madelung rule (n+l) for ordering. 2. Pauli exclusion: No two electrons can have the same four quantum numbers, so max 2 per orbital with opposite spins. 3. Hund's rule: Within a subshell, fill each orbital singly with parallel spins before pairing. These three rules give the unique ground-state configuration of every atom.
What's the difference between full and noble-gas shorthand?
Full configuration lists every subshell explicitly: sodium = 1s² 2s² 2p⁶ 3s¹. Noble-gas shorthand uses the previous noble gas as a base: sodium = [Ne] 3s¹. The noble-gas form is much more compact for heavy elements — uranium full would be 25+ subshells, but [Rn] 5f³ 6d¹ 7s² is way easier to write. Both forms convey identical information.
Why is chromium [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s²?
Half-filled subshell stability. A 3d⁵ configuration has all five d orbitals singly occupied with parallel spins — maximum total spin and maximum exchange energy (a quantum-mechanical stabilization). The energy gain from completing the half-filled d outweighs the energy cost of leaving 4s singly occupied. Copper ([Ar] 3d¹⁰ 4s¹) follows the same logic for filled (d¹⁰) stability.
How do I find valence electrons from the configuration?
Valence electrons are those in the outermost (highest n) shell. For main-group elements (s and p blocks), it's straightforward: nitrogen [He] 2s² 2p³ has 5 valence electrons (2 from 2s + 3 from 2p). For transition metals (d-block), include both the (n)s and (n−1)d electrons: iron [Ar] 3d⁶ 4s² has 8 valence electrons. The actual chemical valence (oxidation states) is more nuanced — Fe commonly forms +2 and +3 ions, not +8.
Why does 4s fill before 3d?
Because 4s has a lower (n + l) value: 4 + 0 = 4 for 4s, vs 3 + 2 = 5 for 3d. The Madelung rule says lower (n + l) fills first. So we get [Ar] 4s² 3d¹ for scandium, not [Ar] 3d³. Counterintuitive twist: after both 4s and 3d are filled, the 4s electrons actually become higher in energy than the 3d electrons — which is why transition metals always lose 4s first when forming cations (Fe → Fe²⁺ is [Ar] 3d⁶, not [Ar] 3d⁴ 4s²).
What does the orbital diagram show?
Each box represents one orbital. Up-arrows (↑) and down-arrows (↓) represent electrons with opposite spins. Within a subshell, electrons fill singly with parallel spins (all up-arrows) before any orbital gets a second electron — this is Hund's rule. Nitrogen's 2p³, for example, shows 3 separate boxes each with one up-arrow, not 1 box with up+down + 1 with up + 1 empty. The diagram makes the rules visible.
What are the four quantum numbers?
Every electron in an atom is described by four numbers: n (principal — energy level: 1, 2, 3, ...), l (azimuthal — subshell shape: 0=s, 1=p, 2=d, 3=f), mₗ (magnetic — orbital orientation, takes values from −l to +l), and mₛ (spin: +½ or −½). The Pauli exclusion principle says no two electrons in the same atom can share all four — which is why each orbital holds at most 2 electrons.
How do I find the configuration of an ion?
For cations (positive ions), remove electrons from the highest principal quantum number first, NOT from where they were last filled. So Fe ([Ar] 3d⁶ 4s²) loses both 4s electrons first → Fe²⁺ = [Ar] 3d⁶. Fe³⁺ = [Ar] 3d⁵. For anions (negative ions), simply add electrons to the next available subshell following Aufbau: F (1s² 2s² 2p⁵) + 1 e⁻ → F⁻ = 1s² 2s² 2p⁶ = [Ne].
Why are noble gases so unreactive?
Because they have completely filled valence shells. He = 1s²; Ne = [He] 2s² 2p⁶; Ar = [Ne] 3s² 3p⁶; etc. Filled shells are the most stable electronic arrangements possible — no driving force to gain or lose electrons. This is the basis of the octet rule: other elements gain/lose/share electrons to achieve a noble-gas-like 8-valence-electron configuration.
Are there configurations beyond uranium?
Yes — elements 93 (neptunium) through 118 (oganesson) have predicted ground-state configurations, but for super-heavy elements (Z > 100) relativistic effects become significant and the Aufbau order is no longer fully reliable. The configurations of elements 104–118 are partly experimental, partly theoretical, and various sources disagree on exact configurations. This calculator covers H through U — the 92 naturally occurring elements where configurations are well-established.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our chemistry tools team curates the ground-state electron configurations of all 92 naturally occurring elements (H through U) — including the 19 known Aufbau anomalies (Cr, Cu, Mo, Ag, Au, Pd, Pt, etc.) where extra stability of half-filled or filled subshells overrides the standard filling order. Output includes noble-gas shorthand, full subshell occupations, orbital filling diagram showing Hund's-rule electron distribution, atomic-number/period/group/block placement, and an explanation of any anomaly affecting your chosen element.

Quantum ChemistryPeriodic Table & Aufbau PrincipleSoftware Engineering Team

Disclaimer

Configurations shown are ground-state — what you'd find in IUPAC tables and most chemistry textbooks. Excited-state and ionic configurations differ. The 19 known Aufbau anomalies are noted explicitly when they apply. For super-heavy elements (Z > 92), relativistic effects make configurations less certain and theoretical predictions vary; this calculator covers H through U where the configurations are well-established.