INORGANIC CHEMISTRYAtomic PropertiesChemistry Calculator
⚛️

Electron Configuration: Aufbau, Hund, Pauli

Electron configuration describes how electrons fill orbitals. Aufbau: fill lowest energy first. Hund's rule: maximize unpaired in degenerate orbitals. Pauli: max 2 e⁻ per orbital, opposite spin. Notation: 1s²2s²2p⁶...

Concept Fundamentals
—
Config
—
Valence
—
Noble
s p d f
Orbitals
Calculate Electron ConfigurationAufbau | Noble gas notation | Valence electrons

Why This Chemistry Calculation Matters

Why: Electron configuration determines chemical properties, bonding, and periodic trends. Foundation for understanding reactivity and spectroscopy.

How: Enter element symbol or atomic number. Configuration follows Aufbau order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p.

  • ●Aufbau: fill lowest energy first.
  • ●Hund: maximize unpaired in degenerate orbitals.
  • ●Pauli: max 2 e⁻ per orbital, opposite spin.
Sources:IUPAC Periodic TableNIST Atomic Data

Sample Examples

⚛️ Carbon (C)

Neutral carbon atom - 6 electrons, configuration: 1s² 2s² 2p²

Click to use this example

➕ Sodium Ion (Na⁺)

Sodium cation - lost 1 electron, noble gas configuration

Click to use this example

➖ Chloride Ion (Cl⁻)

Chloride anion - gained 1 electron, noble gas configuration

Click to use this example

🔩 Iron (Fe)

Transition metal - 26 electrons, includes 3d orbitals

Click to use this example

🔩 Iron(II) Ion (Fe²⁺)

Iron cation - lost 2 electrons from 4s orbital

Click to use this example

🔴 Oxygen (O)

Neutral oxygen - 8 electrons, configuration: 1s² 2s² 2p⁴

Click to use this example

🦴 Calcium (Ca)

Alkaline earth metal - 20 electrons, [Ar] 4s²

Click to use this example

Enter Element Data

Calculation Mode

Choose how to specify the element

Element Selection

Select an element from the periodic table

Ion Configuration (Optional)

Enter ionic charge (0 for neutral atom, positive for cations, negative for anions)

Display Options

Display visual orbital diagram

For educational and informational purposes only. Verify with a qualified professional.

🔬 Chemistry Facts

⚛️

Aufbau: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p.

— Quantum

⚡

Hund's rule: maximize unpaired electrons in degenerate orbitals.

— IUPAC

🔬

Pauli exclusion: max 2 e⁻ per orbital, opposite spin.

— Quantum

📐

Noble gas notation: [He]2s²2p³ for N.

— Inorganic

What is Electron Configuration?

Electron configuration describes how electrons are distributed among the atomic orbitals of an atom or ion. It follows three fundamental principles: the Aufbau principle, the Pauli exclusion principle, and Hund's rule. Understanding electron configuration is crucial for predicting chemical properties, bonding behavior, and periodic trends.

Aufbau Principle

Electrons fill orbitals in order of increasing energy, starting with the lowest energy orbitals first.

Pauli Exclusion Principle

No two electrons in an atom can have the same set of four quantum numbers. Each orbital can hold a maximum of 2 electrons with opposite spins.

Hund's Rule

When filling degenerate orbitals (same energy), electrons occupy separate orbitals with parallel spins before pairing up.

How to Calculate Electron Configuration

Step 1: Determine Total Electrons

For neutral atoms: Total electrons = Atomic number (Z)

For ions: Total electrons = Atomic number - Ionic charge

Example: Na⁺ has 11 - 1 = 10 electrons

Step 2: Follow Aufbau Order

Fill orbitals in this order:

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

Note: 4s fills before 3d, and 5s fills before 4d (energy order)

Step 3: Apply Orbital Capacity Limits

  • s orbitals: Maximum 2 electrons
  • p orbitals: Maximum 6 electrons (3 orbitals × 2 electrons)
  • d orbitals: Maximum 10 electrons (5 orbitals × 2 electrons)
  • f orbitals: Maximum 14 electrons (7 orbitals × 2 electrons)

Step 4: Write Configuration

Write the configuration with superscripts indicating electron count:

Example: Carbon (Z=6) → 1s² 2s² 2p²

Step 5: Noble Gas Notation (Optional)

Replace the core electron configuration with the preceding noble gas symbol:

Example: Sodium (Na) → [Ne] 3s¹

Noble gases: He, Ne, Ar, Kr, Xe, Rn

When to Use Electron Configuration

Chemical Bonding

  • Predict bond types (ionic vs covalent)
  • Determine oxidation states
  • Understand Lewis structures
  • Predict molecular geometry

Periodic Trends

  • Explain atomic radius trends
  • Understand ionization energy
  • Predict electron affinity
  • Explain electronegativity patterns

Ion Formation

  • Predict which electrons are lost/gained
  • Understand stable ion configurations
  • Explain octet rule exceptions
  • Predict ion charges

Spectroscopy

  • Interpret atomic spectra
  • Understand emission/absorption lines
  • Explain energy level transitions
  • Predict spectral patterns

Key Formulas and Rules

Total Electrons

e = Z - q
where:
e = total electrons
Z = atomic number
q = ionic charge (positive for cations, negative for anions)

For neutral atoms, q = 0, so e = Z

Orbital Capacity

Maximum electrons = 2(2l + 1)
where l is the azimuthal quantum number:
l = 0 (s): 2 electrons
l = 1 (p): 6 electrons
l = 2 (d): 10 electrons
l = 3 (f): 14 electrons

Valence Electrons

Valence electrons = electrons in outermost shell
For main group elements (s and p block):
Valence electrons = electrons in highest n shell
For transition metals (d block):
Valence electrons = (n-1)d + ns electrons

Valence electrons determine chemical reactivity

Core Electrons

Core electrons = Total electrons - Valence electrons
Core electrons are in filled inner shells
They are represented by noble gas notation

Aufbau Energy Order

Energy increases: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s

Note: Lower n + l values fill first; if equal, lower n fills first

Special Cases and Exceptions

Transition Metal Exceptions

Some transition metals have exceptions due to half-filled or fully-filled d subshell stability:

  • Chromium (Cr, Z=24): [Ar] 3d⁵ 4s¹ (not [Ar] 3d⁴ 4s²)
  • Copper (Cu, Z=29): [Ar] 3d¹⁰ 4s¹ (not [Ar] 3d⁹ 4s²)
  • Molybdenum (Mo, Z=42): [Kr] 4d⁵ 5s¹
  • Silver (Ag, Z=47): [Kr] 4d¹⁰ 5s¹

Ion Configuration Rules

When forming ions, electrons are removed or added according to these rules:

  • Cations: Remove electrons from highest n shell first (typically s, then p)
  • Transition metal cations: Remove ns electrons before (n-1)d electrons
  • Anions: Add electrons to highest n shell, following Aufbau order
  • Stable configurations: Ions often achieve noble gas configuration
👈 START HERE
⬅️Jump in and explore the concept!
AI

Related Calculators

Atom Calculator

Calculate atomic number, mass number, and ionic charge from protons, neutrons, and electrons.

Chemistry

Atomic Mass Calculator

Calculate atomic mass from protons and neutrons with binding energy and mass defect analysis.

Chemistry

Average Atomic Mass Calculator

Calculate the weighted average atomic mass from isotope masses and natural abundances. Essential for understanding elemental properties and mass spectrometry...

Chemistry

Bond Order Calculator

Calculate bond order from molecular orbital theory. Determine bonding strength, stability, and magnetic properties of diatomic molecules.

Chemistry

Chemical Name Calculator

Convert between IUPAC names and common names, identify functional groups from chemical formulas, and generate systematic names for organic and inorganic...

Chemistry

Degree of Unsaturation Calculator

Calculate degree of unsaturation (DBE/IHD) from molecular formulas. Determine rings, double bonds, triple bonds, and aromaticity in organic compounds.

Chemistry