Transition Elements (d-Block): Configuration, Properties & Trends - Chemistry | Agrigyan

Electronic configurations of monopositive ions:

• $\text{V}^+: [\text{Ar}]3d^3 4s^1 \implies$ Second electron is removed from $4s^1$ ($IE_2 = 1414\text{ kJ mol}^{-1}$)
• $\text{Cr}^+: [\text{Ar}]3d^5 \implies$ Second electron must be removed from the stable, half-filled $3d^5$ configuration, requiring exceptionally high energy ($IE_2 = 1592\text{ kJ mol}^{-1}$)
• $\text{Mn}^+: [\text{Ar}]3d^5 4s^1 \implies$ Second electron is removed from $4s^1$, leaving a stable half-filled $3d^5$ state ($IE_2 = 1509\text{ kJ mol}^{-1}$)

Colours of hydrated ions in aqueous solutions:

• $\text{VOCl}_2$ dissociates into vanadyl ion $\text{VO}^{2+}$ (oxidation state $+4, 3d^1$), which imparts a characteristic blue colour to the solution.
• $\text{CuCl}_2$ dissociates into copper(II) ion $\text{Cu}^{2+}$ ($3d^9$), which forms hydrated $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}$ and is also blue in colour.
• $\text{FeCl}_2$ ($ ext{Fe}^{2+}$) is pale green.
• $\text{MnCl}_2$ ($ ext{Mn}^{2+}$) is very pale pink / almost colourless.

The maximum oxidation state of first row transition metals increases up to the middle of the series:

• $\text{Sc}: +3$
• $\text{Ti}: +4$
• $\text{V}: +5$
• $\text{Cr}: +6$
• $\text{Mn}: +7$ (in $\text{KMnO}_4$, $\text{Mn}_2\text{O}_7$)
• $\text{Fe}: +6$ (rarely, e.g. ferrate)

Manganese has the valence shell configuration $3d^5 4s^2$, allowing all seven valence electrons to participate in bonding and reaching $+7$, the highest oxidation state in the $3d$ series.