Background: Electronic Configuration ***For Student***

• Electron Configurations

Madelung ordering of atomic orbital energy (energy ordering indicated by the arrows).

Aufbau principle: Electrons will reside in the available orbitals of the lowest possible energy.

Madelung order: Electrons are assigned to atomic orbitals in the order of increasing (n+l) value. For orbitals with the same (n+l) value, first assign electrons to orbitals with lower n.

Pauli’s exclusion principle: Each orbital can accommodate a maximum of two electrons of opposite spin.

Hund’s rule: Electrons will not pair in degenerate orbitals if an empty orbital is available. 

Exception: half-filled or fully filled d subshells have additional stability – hence electron configurations ns²(n-1)d⁴ and ns²(n-1)d⁸  might be replaced by ns¹(n-1)d⁵ and (n-1)d¹⁰ respectively

(d-block) cations are formed by removing electrons first from the shell with the highest value of n.

Condensed electron configuration: The electron configurations of all elements except hydrogen and helium can be represented using a noble gas core.