The first ionization energy of O is lower than that of N
CHEMISTRY · Single correct · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
The first ionization energy of O is lower than that of N, even though O is to the right of N in the same period. Which of the following best accounts for this anomaly?
(a) O has a larger atomic radius than N, so its valence electrons are farther from the nucleus and easier to remove.
(b) Additional shielding from O's extra inner electrons counters its greater nuclear charge, resulting in a weaker attraction for its valence electrons.
(c) In O, pairing of electrons in a 2p orbital introduces additional electron–electron repulsion, lowering the energy required to remove one of them.
(d) The 2p subshell in N is completely filled, whereas the 2p subshell in O is only partially filled, making electrons in O less stable.