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Electron Configuration Calculator

Determine the full electron configuration and noble gas shorthand notation for any element. Enter an atomic number (1-118) to see orbital filling using the aufbau principle, with exceptions for chromium, copper, and other irregular elements.

Enter the atomic number of the element (1 for Hydrogen through 118 for Oganesson)

What is a Electron Configuration Calculator?

The electron configuration of an atom describes the distribution of its electrons among the various atomic orbitals. Understanding electron configurations is foundational to chemistry because it determines an element's chemical behavior, bonding characteristics, and position in the periodic table. Electrons fill orbitals starting from the lowest available energy level, following three key principles: the aufbau principle (electrons occupy the lowest energy orbital available), the Pauli exclusion principle (no two electrons can have the same set of four quantum numbers, limiting each orbital to two electrons with opposite spins), and Hund's rule (electrons fill degenerate orbitals singly before pairing). This free electron configuration calculator instantly generates the full orbital notation and noble gas shorthand for any of the 118 known elements, including common exceptions like chromium and copper where half-filled and fully-filled d subshells provide extra stability.

Formula

Filling order: 1s→2s→2p→3s→3p→4s→3d→4p→5s→⋯\text{Filling order: } 1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p \rightarrow 5s \rightarrow \cdots

Electrons fill orbitals in order of increasing energy following the aufbau (building-up) principle. The filling order is determined by the (n + l) rule: orbitals with lower (n + l) values fill first, and when two orbitals have the same (n + l), the one with the lower n fills first. The maximum number of electrons per subshell is: s = 2, p = 6, d = 10, f = 14.

How to Calculate

  1. 1

    Identify the element and its atomic number Z (which equals the number of electrons in a neutral atom).

  2. 2

    Write out the aufbau filling order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

  3. 3

    Fill each orbital with electrons up to its maximum capacity (s=2, p=6, d=10, f=14) until all Z electrons have been placed.

  4. 4

    Check for known exceptions (e.g., Cr is [Ar] 3d5 4s1 instead of [Ar] 3d4 4s2 due to half-filled d orbital stability).

  5. 5

    Write the full configuration and optionally abbreviate the core electrons using the nearest preceding noble gas in brackets.

Worked Examples

Electron Configuration of Carbon (Z = 6)

Input: 6

  1. Carbon has 6 electrons to place.
  2. Fill 1s: 1s² (2 electrons used, 4 remaining)
  3. Fill 2s: 2s² (2 electrons used, 2 remaining)
  4. Fill 2p: 2p² (2 electrons used, 0 remaining)
  5. Full configuration: 1s² 2s² 2p²
  6. Noble gas shorthand: [He] 2s² 2p²

Result: 1s² 2s² 2p² or [He] 2s² 2p²

Electron Configuration of Iron (Z = 26)

Input: 26

  1. Iron has 26 electrons to place.
  2. Fill 1s² 2s² 2p⁶ 3s² 3p⁶ (uses 18 electrons, 8 remaining)
  3. Fill 4s: 4s² (2 electrons used, 6 remaining)
  4. Fill 3d: 3d⁶ (6 electrons used, 0 remaining)
  5. Full configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
  6. Noble gas shorthand: [Ar] 4s² 3d⁶

Result: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ or [Ar] 4s² 3d⁶

Electron Configuration of Silver (Z = 47) — Exception

Input: 47

  1. Silver has 47 electrons. Standard aufbau predicts [Kr] 5s² 4d⁹.
  2. However, Ag is an exception: one electron from 5s shifts to 4d to achieve a fully-filled d¹⁰ subshell.
  3. Actual configuration: [Kr] 5s¹ 4d¹⁰
  4. Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d¹⁰

Result: [Kr] 5s¹ 4d¹⁰

Frequently Asked Questions

The aufbau principle (from German 'Aufbau' meaning 'building up') states that electrons fill atomic orbitals starting from the lowest energy level and moving to higher ones. The filling order follows the (n + l) rule, where n is the principal quantum number and l is the azimuthal quantum number. Orbitals with lower (n + l) values are filled first.
Chromium (Cr) and copper (Cu) are classic exceptions to the aufbau principle. Chromium has the configuration [Ar] 3d5 4s1 instead of the expected [Ar] 3d4 4s2, and copper has [Ar] 3d10 4s1 instead of [Ar] 3d9 4s2. This occurs because half-filled (d5) and fully-filled (d10) d subshells have extra stability due to exchange energy and symmetrical electron distribution.
Noble gas shorthand (or core notation) simplifies electron configurations by replacing the inner core electrons with the symbol of the preceding noble gas in brackets. For example, sodium (Na, Z=11) has the full configuration 1s2 2s2 2p6 3s1, which can be written as [Ne] 3s1 since neon accounts for the first 10 electrons.
Hund's rule states that when filling orbitals of equal energy (degenerate orbitals), electrons occupy them singly with parallel spins before pairing up. For example, in the 2p subshell of nitrogen (3 electrons in 2p), each of the three 2p orbitals gets one electron before any pairing occurs. This minimizes electron-electron repulsion and lowers the total energy.
The structure of the periodic table directly reflects electron configurations. Elements in the s-block (Groups 1-2) have their outermost electrons in s orbitals. The p-block (Groups 13-18) fills p orbitals. The d-block (transition metals, Groups 3-12) fills d orbitals. The f-block (lanthanides and actinides) fills f orbitals. Elements in the same group have similar valence electron configurations, which explains their similar chemical properties.

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