Question

Four successive members of the first row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy?

• A. Vanadium (Z = 23)
• B. Chromium (Z = 24)
• C. Iron (Z = 26)
• D. Manganese (Z = 25)

Answer 1

Answer: (D)

Manganese (Z = 25)

Answer 2

${ }_{23} V =1 s^{2}\, 2 s^{2}\, 2 p^{6},\, 3 s^{2} \,3 p^{6}\, 3 d^{3}, \,4 s^{2}$ ${ }_{24} Cr =1 s^{2}\, 2 s^{2}\, 2 p^{6},\, 3 s^{2}\, 3 p^{6} \,3 d^{5},\, 4 s^{1}$ ${ }_{26} Fe =1 s^{2}\, 2 s^{2}\, 2 p^{6},\, 3 s^{2}\, 3 p^{6}\, 3 d^{6},\, 4 s^{2}$ ${ }_{25} Mn =1 s^{2}\, 2 s^{2} \,2 p^{6}, \,3 s^{2}\, 3 p^{6}\, 3 d^{5},\, 4 s^{2}$ Third electron which is removed in third ionisation enthalpy belongs to $3 d$ -subshells. It means in all elements, shell and subshells are same therefore, required amount of energy is pased upon stability of $d$-subshell. Hence, $Mn$ hows highest third ionisation energy.