In the second row of the periodic table, \(\mathrm{Be}, \mathrm{N}\), and \(\mathrm{Ne}\) all have endothermic (unfavorable) electron affinities, whereas the other second-row elements have exothermic (favorable) electron affinities. Rationalize why Be, \(\mathrm{N}\), and Ne have unfavorable electron affinities.

Electron affinity is the energy change associated with adding an electron to a gaseous atom. The more negative the value, the more exothermic the process, which indicates that the atom has a favorable tendency to gain an electron. Conversely, elements with endothermic electron affinities have a positive value, meaning that energy must be provided for the atom to accept an electron, making the process unfavorable.

To understand the reason behind the endothermic electron affinity of Be, N, and Ne, we should analyze their electronic configurations. Be: \[1s^2 \ 2s^2\] N: \[1s^2 \ 2s^2 \ 2p^3\] Ne: \[1s^2 \ 2s^2 \ 2p^6\]

Let's now relate the electronic configurations to the electron affinity of these elements: 1. Be: Beryllium has a completely filled 2s subshell. When an electron is added to the beryllium atom, it will go to the 2p subshell. However, adding an electron to the 2p subshell would break the stability of the completely filled 2s subshell, so the electron affinity for Be is endothermic. 2. N: Nitrogen has exactly half-filled 2p subshell, which is considered to be a stable configuration. Adding an electron to nitrogen would disrupt this stable half-filled configuration, resulting in an endothermic electron affinity. 3. Ne: Neon has a completely filled 2p subshell, and the next available subshell for an additional electron would be the 3s subshell. However, this requires more energy than is released in the process, so the electron affinity for Ne is endothermic. In summary, Be, N, and Ne have endothermic electron affinities because the addition of an electron would disrupt their stable electronic configurations, requiring energy to accommodate the extra electron. Other elements in the second row have exothermic electron affinities because their electronic configurations become more stable when gaining an electron.