First Transition Series — Oxidation States • Hund • IE Graph Line/Bar

Electronic Configuration

Iron — Z=26

[Ar] 4s² 3d⁶

4s subshell

3d subshell — Hund's rule: single ↑ fill first, then ↓ pairing

↑ spin-up ↓ spin-down Removal order: 4s → 3d

Oxidation State

Successive Ionization Energies IE₁–IE₉ (kJ/mol)

NIST / ChemLin. 1 eV = 96.485 kJ·mol⁻¹. Red = Ar-core break.

Example Compounds for this oxidation state

Colors = characteristic aqueous / solid ion colors.

Ionization Energy Graph — till Ar-core break

log scale show Ar break

All known oxidation states

Variable oxidation states: 4s ≈ 3d in energy. Max oxidation rises Sc→Mn (+7) then falls to Zn (+2). d⁵ / d¹⁰ extra stability → Cr [Ar] 4s¹3d⁵, Cu [Ar] 4s¹3d¹⁰.

First Transition Series — Summary Poster — Sc to Zn

4s removed before 3d. IE kJ/mol NIST/ChemLin. Red = Ar-core break.