Question

Select the correct order of 2nd ionization energy of C, N, O, and F.

• A. C > N > O > F
• B. N > C > O > F
• C. C < N < O < F
• D. O > F > N > C

Answer 1

Answer: (D)

O > F > N > C

Consider the configurations of the given elements after the loss of an electron.

$C^{+}$ : $1s^{2}2s^{2}2p^1$

$N^{+}$ : $1s^{2}2s^{2}2p^2$

$O^{+}$ : $1s^{2}2s^{2}2p^3$

$F^{+}$ : $1s^{2}2s^{2}2p^4$

We notice that $O$ has a half-filled orbital and hence has the highest I.E. among these. Also, carbon can lose an electron easily. Fluorine will reach a half-filled configuration upon the loss of an electron. Hence, the order is $O>F>N>C$.