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The d-block elements occupy groups 3-12 with general configuration (n-1)d^(1-10) ns^(0-2). The 3d series (Sc to Zn) has two key anomalies: Cr = [Ar]3$d^5$ 4$s^1$ (half-filled d stability) and Cu = [Ar]3$d^{10}$ 4$s^1$ (fully-filled d stability).

When forming cations, 4s electrons are lost before 3d despite 4s filling first. This occurs because 3d orbitals contract below 4s in energy once d-electrons are added. $Fe^{2+}$ = [Ar]3$d^6$, NOT [Ar]3$d^4$ 4$s^2$. $Cu^{2+}$ = [Ar]3$d^9$.

The maximum oxidation state increases from Sc(+3) to Mn(+7), equalling the total number of (ns + (n-1)d) electrons. After Mn, the maximum achievable OS decreases because electrons are too tightly held. The +2 state (loss of $ns^2$) is nearly universal across the series. Stability of +2 increases across the series, with $Mn^{2+}$ ($d^5$) and $Zn^{2+}$ ($d^{10}$) being exceptionally stable.

Higher oxidation states are stabilised by electronegative ligands ($F^-$, $O^{2-}$) forming covalent bonds. Lower oxidation states are stabilised by pi-acceptor ligands (CO, $CN^-$) through backbonding. This interplay between oxidation state and ligand type is fundamental to understanding transition metal chemistry.