Periodic TableHard
Question
The correct order of second ionisation potential of carbon, nitrogen, oxygen and fluorine is :
Options
A.C > N > O > F
B.O > N > F > C
C.O > F > N > C
D.F > O > N > C
Solution
On the basis of electronic configuration and effective nuclear charge. The order of I. E2 values may be explained as given below.
E. C. of X(Q, F, N, C), X+ and X2+ are given below:

8O : ls2, 2s2, 2p4 ls2, 2s2, 2p3 ls2, 2s2, 2p2
9F : ls2, 2s2, 2p5 ls2, 2s2, 2p4 ls2, 2s2, 2p3
7N : ls2, 2s2, 2p3 ls2, 2s2, 2p2 ls2, 2s2, 2p1
6C : ls2, 2s2, 2p2 ls2, 2s2, 2p1 ls2, 2s2, 2p0
I. E2 value for O is exceptionally higer because E. C. of O+ is half filled and so more stable. Among F+, N+ and C+ removal of electron from F+ requires maximum energy because it has maximum ENC. On the other hand C+ has least ENC, so it needs least energy for the removal of II electron.
E. C. of X(Q, F, N, C), X+ and X2+ are given below:

8O : ls2, 2s2, 2p4 ls2, 2s2, 2p3 ls2, 2s2, 2p2
9F : ls2, 2s2, 2p5 ls2, 2s2, 2p4 ls2, 2s2, 2p3
7N : ls2, 2s2, 2p3 ls2, 2s2, 2p2 ls2, 2s2, 2p1
6C : ls2, 2s2, 2p2 ls2, 2s2, 2p1 ls2, 2s2, 2p0
I. E2 value for O is exceptionally higer because E. C. of O+ is half filled and so more stable. Among F+, N+ and C+ removal of electron from F+ requires maximum energy because it has maximum ENC. On the other hand C+ has least ENC, so it needs least energy for the removal of II electron.
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