Electron Configuration Calculator

Determine the ground-state electron configuration (spdf notation) for any element on the periodic table using the Madelung rule.

Atomic Number (Z)

Electron Configuration

1s2 2s2 2p6 3s2 3p6 4s2 3d6

Periodic Table Blockd-block (Transition Metals)

Valence Shell Leveln = 4

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Mapping the Architecture of Atoms

An atom is not just a messy cloud of electrons orbiting a nucleus. Electrons exist in highly structured, mathematical territories called orbitals.

The Electron Configuration is the standardized notation that maps exactly where every single electron lives inside an atom. Understanding this map is the fundamental key to predicting how an atom will react, bond, and behave magnetically.

The Rules of the Map

To build the electron configuration for any element, you must fill the atomic "hotel" starting from the lowest energy basement and working your way up, following three universal rules:

The Aufbau Principle: Electrons always fill the lowest energy orbitals first before moving to higher ones. (1s fills before 2s).
The Pauli Exclusion Principle: A single orbital room can hold a maximum of 2 electrons, and they must have opposite spins (up and down).
Hund's Rule: When filling a suite of identical rooms (like the three 2p orbitals), electrons will place themselves in empty rooms first before pairing up. (They prefer having their own room).

The Orbital Capacities

The periodic table is divided into distinct "blocks" based on the type of orbital being filled:

s-orbitals: Can hold a maximum of 2 electrons. (Groups 1 & 2)
p-orbitals: Can hold a maximum of 6 electrons. (Groups 13-18)
d-orbitals: Can hold a maximum of 10 electrons. (Transition Metals)
f-orbitals: Can hold a maximum of 14 electrons. (Lanthanides & Actinides)

The Diagonal Rule (Madelung Energy Ordering Rule)

Because energy levels overlap as they get further from the nucleus, the filling order gets complicated. The 4s orbital is actually slightly lower in energy than the 3d orbital, so 4s fills first!

The standard filling order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ ...

Where:

1, 2, 3...=

Principal Quantum Number (Energy Level)

s, p, d, f=

Orbital Type (Subshell)

Superscript=

Number of electrons in that subshell

Example: Iron (Fe)

Iron has an atomic number of 26, meaning a neutral atom has 26 electrons. We distribute the 26 electrons into the orbitals until we run out:

1s takes 2 (24 left)
2s takes 2 (22 left)
2p takes 6 (16 left)
3s takes 2 (14 left)
3p takes 6 (8 left)
4s takes 2 (6 left)
3d takes the remaining 6.

Final Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

Frequently Asked Questions

Writing out full configurations gets tedious for large elements. Chemists use shorthand by substituting the inner 'core' electrons with the symbol of the previous noble gas in brackets. For Iron (Fe), the core [1s² 2s² 2p⁶ 3s² 3p⁶] is identical to Argon, so the shorthand is simply [Ar] 4s² 3d⁶.

Chromium is a famous exception to the Aufbau principle. Instead of [Ar] 4s² 3d⁴, its true configuration is [Ar] 4s¹ 3d⁵. A half-filled d-subshell (5 electrons in 5 orbitals) is exceptionally stable, so an electron 'jumps' from the 4s to the 3d to achieve this stable state.

Similar to Chromium, Copper achieves maximum stability by completely filling its d-subshell. Instead of the expected [Ar] 4s² 3d⁹, an electron shifts to create the highly stable configuration [Ar] 4s¹ 3d¹⁰.

Valence electrons are the electrons located in the outermost principal energy level (the highest number). In the configuration for Iron (4s² 3d⁶), the highest energy level is 4. Therefore, Iron only has 2 valence electrons (the 4s²), even though the 3d orbital was filled last.

For negative ions (anions), you simply add the extra electrons to the next available orbital. For positive ions (cations), you remove electrons. CRITICALLY: For transition metals, you always remove electrons from the highest 's' orbital before removing from the 'd' orbital. Fe²⁺ loses its 4s electrons first, becoming [Ar] 3d⁶.

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