Correct order of first ionization energy of Li, Be, C, B, N, O, F

Question

Among the following the isoelectronic species are
I. $Mg^{2+}, Al^{3+}, F^-$
II. $O^{2-}, F^-, N^{3-}$
III. $K^+, Ca^{2+}, Sc^{3+}$
IV. $Mn^{2+}, Fe^{3+}, V^{3+}$

Answer 1

Correct order of first ionization energy of Li, Be, C, B, N, O, F:

F > N > O > C > Be > B > Li

Explanation:
Ionization energy generally increases across a period due to increase in nuclear charge.

Exception 1: Be > B
Be has fully filled 2s orbital, so more stable.

Exception 2: N > O
N has half-filled 2p orbitals (extra stability), while O has paired electrons causing repulsion.

Correct order of first ionization energy of Li, Be, C, B, N, O, F

Solution and Explanation

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