How does this electron configuration calculator work?

The calculator uses the Aufbau principle, Pauli exclusion principle, and Hund's rule to fill orbitals in the correct energy order. It supports all elements up to atomic number 118, shows the full and noble gas shorthand configurations, an orbital box diagram, and quantum numbers for the last electron.

Does the calculator handle exceptions like chromium and copper?

Yes. Several transition metals and f-block elements have experimentally observed configurations that differ from the simple Aufbau pattern. The calculator includes a built-in list of these exceptions and uses the experimentally accepted configurations for them.

What are the four quantum numbers for an electron?

The four quantum numbers are: n (principal quantum number, energy level), l (angular momentum, subshell type s, p, d, f), mₗ (magnetic quantum number, specific orbital within a subshell), and mₘ (spin quantum number, +1/2 or -1/2). The calculator reports these for the last electron in the configuration.

How do I write noble gas shorthand electron configurations?

To write noble gas shorthand, replace the configuration of the previous noble gas with its symbol in brackets, then add the remaining subshells. For example, sulfur (Z = 16) has full configuration 1s2 2s2 2p6 3s2 3p4, which becomes [Ne] 3s2 3p4. The calculator shows both full and shorthand forms.

Electron Configuration Calculator

Get the full electron configuration, noble gas shorthand, orbital box diagram, and quantum numbers for any element up to Z = 118.

Electron configuration finder

Element name, symbol, or atomic number

Supports H–Og (1–118). You can also pick from the dropdown.

Quick select element

Show orbital box diagram

Element summary

Element:: –
Symbol:: –
Atomic number (Z):: –
Period / Group:: –
Block:: –

Electron configuration

Full configuration

–

Noble gas shorthand

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Valence shell & quantum numbers (last electron)

Valence shell: –

Valence electrons: –

Highest occupied subshell: –

n (principal): –

l (subshell): –

m_l (orbital): –

m_s (spin): –

Orbital box diagram (Aufbau filling)

Hund's rule & Pauli exclusion visualized

No element selected yet.

How to use the electron configuration calculator

Type an element name (oxygen), symbol (O), or atomic number (8) in the input box, or pick it from the dropdown.
Click “Calculate configuration”.
Read:
- the full electron configuration,
- the noble gas shorthand,
- a visual orbital box diagram,
- valence shell and valence electrons,
- the four quantum numbers for the last electron.
Toggle “Show orbital box diagram” off if you only need the text configuration.

What is electron configuration?

Electron configuration describes how electrons are distributed among the orbitals of an atom. For example, the configuration of oxygen (Z = 8) is:

1s² 2s² 2p⁴

Each term has three parts:

Number (1, 2, 3, …) = principal energy level (n).
Letter (s, p, d, f) = subshell type (shape of the orbital).
Superscript = number of electrons in that subshell.

Rules used by the calculator

1. Aufbau principle (order of filling)

Orbitals are filled from lowest to highest energy. The typical order up to 7p is:

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

The calculator follows this order and stops when the total number of electrons equals the atomic number Z, unless an experimentally known exception applies.

2. Pauli exclusion principle

Each orbital can hold at most two electrons, and they must have opposite spins. In the orbital box diagram, each box represents one orbital and can contain at most two arrows (↑↓).

3. Hund’s rule

For subshells with multiple orbitals (p, d, f), electrons fill empty orbitals singly with parallel spins before pairing up. That’s why, for example, nitrogen (2p³) is drawn as:

2p: ↑ ↑ ↑

Full vs. noble gas shorthand configuration

Full configurations list every occupied subshell from 1s onward. Noble gas shorthand replaces the inner, filled shells with the symbol of the previous noble gas in brackets.

Example: sulfur (Z = 16)

Full: 1s² 2s² 2p⁶ 3s² 3p⁴
Shorthand: [Ne] 3s² 3p⁴

The calculator automatically finds the correct noble gas core and shows both forms.

Quantum numbers for the last electron

Every electron in an atom is described by four quantum numbers:

n – principal quantum number (1, 2, 3, …), the main energy level.
l – angular momentum quantum number (0 = s, 1 = p, 2 = d, 3 = f).
m_l – magnetic quantum number (−l … +l), which orbital within the subshell.
m_s – spin quantum number (+½ or −½).

The calculator reports these for the last electron added (the “outermost” electron in the Aufbau picture), which is often the one involved in chemical changes.

Common exceptions to simple Aufbau filling

Some transition metals and f-block elements have ground-state configurations that differ from the simple Aufbau prediction. This is due to subtle energy differences and extra stability of half-filled or fully filled subshells.

Famous examples include:

Chromium (Cr, Z = 24) – expected: [Ar] 4s² 3d⁴, actual: [Ar] 4s¹ 3d⁵.
Copper (Cu, Z = 29) – expected: [Ar] 4s² 3d⁹, actual: [Ar] 4s¹ 3d¹⁰.
Silver (Ag, Z = 47) – [Kr] 4d¹⁰ 5s¹.
Gold (Au, Z = 79) – [Xe] 4f¹⁴ 5d¹⁰ 6s¹.

The calculator includes a curated list of such exceptions and uses the experimentally accepted configurations for them, so your answers match standard chemistry references.

Study tips for mastering electron configurations

Memorize the order of subshell energies up to 7p using an Aufbau diagram or mnemonic.
Practice writing configurations for the first 20 elements until it feels automatic.
Use noble gas shorthand for heavier elements to keep work manageable.
Pay special attention to transition metals and their common exceptions.
Relate configurations to periodic trends (valence electrons, block, group number).