Electrochemical Anomalies

Anomalous Values Matrix: $$\begin{aligned} \text{The Copper Anomaly:} &\quad E^\circ(\text{Cu}^{2+}/\text{Cu}) = +0.34\text{ V} \quad (\text{Only positive value in } 3d \text{ series}) \\ \text{Mn and Zn Drops:} &\quad E^\circ(\text{Mn}^{2+}/\text{Mn}) \text{ and } E^\circ(\text{Zn}^{2+}/\text{Zn}) \text{ are more negative than expected.} \end{aligned}$$

Concept: A positive copper value means it cannot liberate hydrogen gas ($$\text{H}_2$$) from non-oxidizing acids.

Notation:

• $$\text{Cu}^{2+}$$ stability is limited by high ionization cost;
• $$\text{Mn}^{2+}$$ dip is driven by stable half-filled $$d^5$$ shells;
• $$\text{Zn}^{2+}$$ dip is driven by stable fully-filled $$d^{10}$$ shells.