JEE MainChemistryClassification of Elements and Periodicity in Properties
The correct decreasing order of the second ionization enthalpies ( IE₂ ) for the elements C, N, O, and F is
Options
- AO > F > N > C
- BF > O > N > C
- CN > O > F > C
- DC > N > O > F
Correct answer
A. O > F > N > C
Step-by-step solution
The second ionization enthalpy ( IE₂ ) is the energy required to remove an electron from the monovalent cation ( M ^+ ) of an element. The electronic configurations of the unipositive cations are: C ^+ : 1s^2 2s^2 2p^1 N ^+ : 1s^2 2s^2 2p^2 O ^+ : 1s^2 2s^2 2p^3 F ^+ : 1s^2 2s^2 2p^4 Generally, ionization enthalpy increases from left to right across a period due to an increase in effective nuclear charge. This gives the expected order C ^+ However, the O ^+ cation has a stable, exactly half-filled 2p^3 configuratio