Four successive members of the first two transition elements are listed below with their atomic numbers.…

Four successive members of the first two transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionisation enthalpy?
  1. vanadium $(\mathrm{Z}=23)$
  2. chromium $(\mathrm{Z}=24)$
  3. manganese $(\mathrm{Z}=25)$
  4. iron $(Z=26)$

Solution

$\mathrm{V}^{2+}(21)[\mathrm{Ar}]^{18} 3 d^3 4 s^0$ $\mathrm{Cr}^{2+}$ (22) $[\mathrm{Ar}]^{18} 3 d^4 4 s^0$ $\mathrm{Mn}^{2+}$ (23) $[\mathrm{Ar}]^{18} 3 d^5 4 s^0$ $\mathrm{Fe}^{2+}(24) \quad[\mathrm{Ar}]^{18} 3 d^5 4 s^1$ The value of the third ionization enthalpy will be the largest in the case of manganese as the electrons in the orbitals are in half-filled stable electronic configuration and a very large amount of energy is required to overcome this effect.

Asked in: NEET 2005

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