Question

which of the following species releases the most energy when an electron is added to it
ar
o
o-
n
f-

Explanation:

• Argon (Ar): It has a full - shell electron configuration (\(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\)). Adding an electron would place it in a higher - energy \(4s\) orbital, and it is energetically unfavorable. The electron - affinity of noble gases is either positive (energy is required to add an electron) or close to zero.
• Oxygen (O): The electron - configuration of \(O\) is \(1s^{2}2s^{2}2p^{4}\). When an electron is added to \(O\), it forms \(O^{-}\) with the electron - configuration \(1s^{2}2s^{2}2p^{5}\). There is an energy release (negative electron - affinity) because the added electron fills a \(2p\) orbital and there is some stabilization due to increased electron density in the valence shell.
• \(O^{-}\): The electron - configuration of \(O^{-}\) is \(1s^{2}2s^{2}2p^{5}\). Adding an electron to form \(O^{2 -}\) (\(1s^{2}2s^{2}2p^{6}\)) is unfavorable. Because of the repulsion between the negatively charged \(O^{-}\) ion and the incoming electron. The electron - affinity of \(O^{-}\) is positive (energy is required to add an electron).
• Nitrogen (N): The electron - configuration of \(N\) is \(1s^{2}2s^{2}2p^{3}\). It has a half - filled \(2p\) sub - shell. Adding an electron to \(N\) (\(1s^{2}2s^{2}2p^{4}\)) disrupts the stable half - filled configuration. The electron - affinity of \(N\) is close to zero because of the repulsion between the incoming electron and the electrons in the \(2p\) orbitals and the loss of the half - filled shell stability.
• \(F^{-}\): The electron - configuration of \(F^{-}\) is \(1s^{2}2s^{2}2p^{6}\), a full - shell configuration. Adding an electron would require placing it in a higher - energy \(3s\) orbital, and it is energetically unfavorable. The electron - affinity of \(F^{-}\) is positive (energy is required to add an electron).

Answer:

O