Question

the reaction for electron affinity for several elements is given. which element would have the most favorable electron affinity?
ca + e⁻ → ca⁻
se + e⁻ → se⁻
kr + e⁻ → kr⁻
ga + e⁻ → ga⁻

Explanation:

Electron affinity is the energy change when an electron is added to a neutral atom; a more favorable (more negative) value means the atom readily accepts an electron.

• Ca (alkaline earth metal) has a filled s-subshell, adding an electron requires placing it in a higher energy p-subshell, so electron affinity is positive (unfavorable).
• Kr is a noble gas with a full valence shell, adding an electron requires a new energy level, so electron affinity is highly positive (very unfavorable).
• Ga has a single electron in its 4p subshell; adding an electron here experiences electron-electron repulsion, leading to a weakly negative or near-zero electron affinity.
• Se (chalcogen) has 4 electrons in its 4p subshell, one electron short of a half-filled p-subshell. Adding an electron stabilizes the atom, resulting in a strongly negative (very favorable) electron affinity.

Answer:

Se + e⁻ → Se⁻