Cr = [Ar]3$d^{5}$ 4$s^{1}$ and Cu = [Ar]3$d^{10}$ 4$s^{1}$ are the two configuration anomalies arising from half-filled and fully-filled d-subshell stability; all other first-row transition metals fill 4s before 3d normally.

$KMnO_{4}$ products by medium: acidic → $Mn^{2+}$ (colourless, 5$e^{-}$); neutral → $MnO_{2}$ (brown, 3$e^{-}$); basic → $MnO_{4}^{2-}$ (green, 1$e^{-}$). $K_{2}Cr_{2}O_{7}$ in acid: orange $Cr_{2}O_{7}^{2-}$ → green $Cr^{3+}$.

Spectrochemical series (weak→strong): $I^{-}$ < $Br^{-}$ < $Cl^{-}$ < $F^{-}$ < $OH^{-}$ < $H_{2}O$ < $NH_{3}$ < en < $NO_{2}^{-}$ < $CN^{-}$ < CO. Strong field → large $\Delta o$ → pairing → low spin → low/zero μ. Weak field → high spin → high μ.

CFT: octahedral — t_{2}g lower, eg higher, $\Delta o$; tetrahedral — e lower, t_{2} higher, $\Delta t$ = 4/9 $\Delta o$ (inverted order, smaller gap, almost always high spin).

Lanthanoid contraction (poor 4f shielding) makes Zr ≈ Hf in size; biological coordination compounds: $Fe^{2+}$ (haemoglobin), $Mg^{2+}$ (chlorophyll), $Co^{3+}$ ($B_{12}$), $Zn^{2+}$ (carbonic anhydrase).