Solution:
Electron gain enthalpy, sometimes called electron affinity, refers to the amount of energy released or spent when an electron is added to a neutral atom in the gas phase to form a negative ion. If the energy is released during the process, the electron gain enthalpy is negative, indicating that the process is exothermic and the element tends to gain an electron more readily. Conversely, when the energy is required to add an electron, the electron gain enthalpy is positive, and the process is endothermic, meaning that the element does not favor gaining an electron.
Generally, nonmetals have more negative electron gain enthalpies because they are more likely to accept electrons to complete their valence electron shells. However, there are exceptions, particularly among the noble gases.
In the context of noble gases like neon (Ne), they already have a complete valence shell and are quite stable. Therefore, adding an electron would require forcing it into an already complete electron shell, which is an unfavorable process requiring energy. Hence, noble gases generally have positive electron gain enthalpies despite being nonmetals.
Let's analyze the options given:
Option A: Ne (Neon) - Neon is a noble gas with a stable electronic configuration of 2s22p6. Therefore, it does not tend to gain electrons, and the process of adding an electron to a neon atom is endothermic, requiring energy. Therefore, neon has a positive electron gain enthalpy.
Option B: I (Iodine) - Iodine is a nonmetal and has a high tendency to gain an electron to complete its valence shell, hence it has large negative electron gain enthalpy.
Option C: S (Sulfur) - Sulfur is another nonmetal which prefers to gain electrons to achieve a stable electron configuration, hence it also has negative electron gain enthalpy.
Option D: O (Oxygen) - Oxygen is highly electronegative and readily gains electrons, resulting in negative electron gain enthalpy.
The element among the options provided that has positive electron gain enthalpy is Ne (Neon), so the correct answer is:
Option A: Ne (Neon)
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