NEETChemistryClassification of Elements and Periodicity in Properties
Consider the second ionisation enthalpies ( IE₂ ) of the first transition series elements. Which of the following represents the correct increasing order of IE₂ for the elements Cr, Mn, Cu, and Zn?
Options
- ACr < Mn < Cu < Zn
- BMn < Cr < Zn < Cu
- CMn < Cr < Cu < Zn
- DCr < Mn < Zn < Cu
Correct answer
B. Mn < Cr < Zn < Cu
Step-by-step solution
The second ionisation enthalpy ( IE₂ ) involves the removal of an electron from the univalent cation ( M^+ ). The electronic configurations of the univalent cations are: Cr ^+ (Z=24) : [ Ar ] 3d^5 Mn ^+ (Z=25) : [ Ar ] 3d^5 4s^1 Cu ^+ (Z=29) : [ Ar ] 3d¹⁰ Zn ^+ (Z=30) : [ Ar ] 3d¹⁰ 4s^1 Removing an electron from Cr ^+ and Cu ^+ requires breaking the extra stability of exactly half-filled ( 3d^5 ) and fully-filled ( 3d¹⁰ ) configurations, respectively. In contrast, removing an electron from Mn ^+ and Zn ^+ involves