Electron Configuration Calculator
This electron configuration calculator instantly shows the distribution of electrons in the orbitals of any of the 118 known periodic table elements. Select an element by name and atomic number to get its complete electron configuration, shorthand (noble gas) notation, atomic mass, valence electron count, and number of unpaired electrons.
Ground State Electron Configuration
Electron configuration notation describes the basic energy levels and sublevels that electrons occupy. Ground state means the atom has the lowest possible energy. The notation follows the pattern: nℓx, where:
- n — principal energy level (shell number, 1 to 7)
- ℓ — subshell type: s (max 2e⁻), p (max 6e⁻), d (max 10e⁻), f (max 14e⁻)
- x — number of electrons in that subshell
For example, Carbon (Z = 6) has the configuration 1s² 2s² 2p²: 2 electrons in the 1s subshell, 2 in the 2s subshell, and 2 in the 2p subshell.
Electron Configuration Chart and Hund's Rule
To write an electron configuration, three rules apply:
- Aufbau Principle — electrons fill orbitals in order of increasing energy:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p - Hund's Rule — within a subshell, electrons occupy each orbital singly before any orbital is doubly occupied. All singly occupied orbitals have the same spin direction.
- Pauli Exclusion Principle — no two electrons in the same atom can have identical quantum numbers. Two electrons sharing an orbital must have opposite spins (↑↓).
How to Write Shorthand (Noble Gas) Notation
The shorthand method replaces the core electron configuration with the symbol of the nearest preceding noble gas in square brackets. For example, Sodium (Na, Z = 11) has the full configuration 1s² 2s² 2p⁶ 3s¹, which can be written as [Ne] 3s¹ because Neon accounts for the first 10 electrons.
Noble gas cores used:
- [He] = 1s² (Z = 2)
- [Ne] = [He] 2s² 2p⁶ (Z = 10)
- [Ar] = [Ne] 3s² 3p⁶ (Z = 18)
- [Kr] = [Ar] 3d¹⁰ 4s² 4p⁶ (Z = 36)
- [Xe] = [Kr] 4d¹⁰ 5s² 5p⁶ (Z = 54)
- [Rn] = [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ (Z = 86)
What Are Valence Electrons?
Valence electrons are the electrons in the outermost shell of an atom (or the outer s, p, and sometimes d subshells for transition metals). They determine the chemical behavior and bonding properties of an element. For example:
- Oxygen (O):
[He] 2s² 2p⁴→ 6 valence electrons - Iron (Fe):
[Ar] 3d⁶ 4s²→ 8 valence electrons (3d + 4s) - Carbon (C):
[He] 2s² 2p²→ 4 valence electrons
Exceptions to the Aufbau Principle
Several elements have configurations that deviate from the expected Aufbau order due to extra stability from half-filled or fully filled d subshells:
- Chromium (Z = 24): Expected
[Ar] 3d⁴ 4s², actual[Ar] 3d⁵ 4s¹(half-filled d is more stable) - Copper (Z = 29): Expected
[Ar] 3d⁹ 4s², actual[Ar] 3d¹⁰ 4s¹(fully filled d is more stable) - Similar exceptions occur for Mo, Nb, Ru, Rh, Pd, Ag, Pt, Au, and several lanthanides and actinides.
Element Blocks on the Periodic Table
- s-block (Groups 1–2 + He): outermost electrons in s subshell
- p-block (Groups 13–18): outermost electrons in p subshell
- d-block (Groups 3–12, transition metals): outermost electrons in d subshell
- f-block (lanthanides + actinides): outermost electrons in f subshell
Examples
| Element | Z | Full Configuration | Shorthand | Valence e⁻ |
|---|---|---|---|---|
| Hydrogen | 1 | 1s¹ | 1s¹ | 1 |
| Carbon | 6 | 1s² 2s² 2p² | [He] 2s² 2p² | 4 |
| Iron | 26 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s² | [Ar] 3d⁶ 4s² | 8 |
| Gold | 79 | …4f¹⁴ 5d¹⁰ 6s¹ | [Xe] 4f¹⁴ 5d¹⁰ 6s¹ | 11 |
| Uranium | 92 | …5f³ 6d¹ 7s² | [Rn] 5f³ 6d¹ 7s² | 6 |
FAQs
- Why does the calculator show exceptions for some elements?
- Elements like Cr, Cu, Mo, Pd, Ag, Au, and Pt have configurations that differ from the Aufbau prediction because half-filled or fully filled d subshells are energetically more stable.
- What is the difference between ground state and excited state?
- Ground state is the lowest energy arrangement. Excited state occurs when an electron absorbs energy and jumps to a higher orbital; this is temporary.
- How many valence electrons can an atom have?
- Main group elements have 1–8 valence electrons. Noble gases have 8 (or 2 for Helium). Transition metals can have more when d electrons are counted.
- What does "unpaired electrons" mean?
- Unpaired electrons are those occupying an orbital alone (one electron per orbital, not paired). They determine whether an atom is paramagnetic (attracted to magnetic fields) or diamagnetic.