Electron Configuration

What is Electron Configuration?

Electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. It describes where electrons are likely to be found around the nucleus.

The Aufbau Principle

The "building up" principle states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels.

The order of filling is:

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

Orbtial Capacities

• s-orbital: Holds max 2 electrons.
• p-orbital: Holds max 6 electrons.
• d-orbital: Holds max 10 electrons.
• f-orbital: Holds max 14 electrons.

Notable Exceptions

This calculator uses the standard Madelung rule. However, real-world chemistry has exceptions due to stability. For example:

• Chromium (Cr, 24): Predicted [Ar] 4s² 3d⁴ → Actual [Ar] 4s¹ 3d⁵ (Half-filled d-shell stability).
• Copper (Cu, 29): Predicted [Ar] 4s² 3d⁹ → Actual [Ar] 4s¹ 3d¹⁰ (Full d-shell stability).