Question

Given beside are the electrode potential values, E° for some of the first row transition elements:

Element	\[\ce{E^\circ_{M^{n+}/M}}\] (V)
V (23)	−1.18
Cr (24)	−0.91
Mn (25)	−1.18
Fe (26)	−0.44
Co (27)	−0.28
Ni (28)	−0.25
Cu (29)	+0.34

Explain the irregularities in these values on the basis of electronic structures of atoms.

Answer 1

The electrode potential values (E°) for the first row transition elements show irregularities due to their electronic configurations:

Element	\[\ce{E^\circ_{M^{n+}/M}}\] (V)	Electronic configuration (Ground state)
V (23)	−1.18	[Ar] 3d3 4s2
Cr (24)	−0.91	[Ar] 3d5 4s1 (half-filled d-subshell)
Mn (25)	−1.18	[Ar] 3d5 4s2
Fe (26)	−0.44	[Ar] 3d6 4s2
Co (27)	−0.28	[Ar] 3d7 4s2
Ni (28)	−0.25	[Ar] 3d8 4s2
Cu (29)	+0.34	[Ar] 3d10 4s1 (filled d-subshell)

1. The stability of partially and fully filled d-subshells is the primary cause of the anomalies in electrode potentials.
2. Compared to vanadium (V) and manganese (Mn), which have higher negative electrode potentials (−1.18 V), chromium (Cr) has a less negative electrode potential (−0.91 V) due to its more stable half-filled 3d⁵ configuration.
3. Because of its completely filled 3d¹⁰ subshell, which is extremely stable and produces a positive electrode potential (+0.34 V), copper (Cu) is less susceptible to oxidation.
4. Elements having less stable electronic structures, such as V and Mn, have higher negative electrode potentials, making them more easily oxidized.
5. As we move from V to Cu, the increased stability of d-electrons leads electrode potentials to become less negative and eventually positive.