Atomic Structure

Magnetic moment depends on number of unpaired electrons, calculated by: Where = number of unpaired electrons. Let's calculate for each: - Fe : Atomic number 26 → Fe = 3d → 4 unpaired electrons - Co : Atomic number 27 → Co = 3d → 3 unpaired electrons - Cr : Atomic number 24 → Cr = 3d → 3 unpaired electrons - Ni : Atomic number 28 → Ni = 3d → 2 unpaired electrons But Cr has only 3 electrons all unpaired in orbitals with no pairing energy losses, thus greater stability and maximum spin-only moment (low pairing). Hence: While Fe has 4 unpaired, it experiences some pairing loss in high-spin cases. So Cr shows more stable unpaired electron configuration.