Answer
The positive electron affinities of beryllium, nitrogen, and neon can be rationalized by the unfavorable electron configurations that would result from adding an electron to these atoms.
Work Step by Step
The electron affinity of an atom is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to form a negatively charged ion. The electron affinity depends on the attraction between the added electron and the nucleus of the atom, as well as the repulsion between the added electron and the electrons already present in the atom.
In the case of the second-row elements, the electron affinities of beryllium, nitrogen, and neon are positive because the added electron would occupy a higher energy level than the existing electrons, resulting in an unstable electron configuration.
For beryllium, the added electron would occupy the 2p orbital, which is higher in energy than the filled 2s orbital. This would result in an electron configuration with two half-filled orbitals, which is less stable than the filled 2s orbital.
For nitrogen, the added electron would occupy the 2p orbital, which is already half-filled. This would result in an electron configuration with three half-filled orbitals, which is also less stable than the filled 2p orbital.
For neon, the added electron would occupy the 2p orbital, which is already filled. This would result in an electron configuration with two half-filled and one filled orbital, which is again less stable than the filled 2p orbital.
Therefore, the positive electron affinities of beryllium, nitrogen, and neon can be rationalized by the unfavorable electron configurations that would result from adding an electron to these atoms.
