Question

Which of the following ionization energy order is incorrect?

• A. $O_2<O$
• B. $N_2>N$
• C. $O<N$
• D. $F_2>F$
• E. none of these

Answer 1

Answer: (D)

$F_2>F$

The order of the ionization energy $F_2>F$ represented by option D is incorrect. When an electron is removed from antibonding molecular orbital such as in $F_2$ molecule, the ionization energy is lower than neutral F atom as less energy is required for removal of an electron from antibonding molecular orbital. Hence, $F_2<F$.. Same is true for oxygen molecule. Thus, $O_2<O$.
However, for nitrogen molecule, the electron is to be removed from bonding molecular orbital which requires higher energy. Hence, $N_2>N$
The order $O<N$ is correct because, in case of N, the electron is to be removed from stable half filled p orbital.