Why group 18 noble gases have positive electron affinity values?

Group 18 noble gases typically have positive electron affinity values because they possess a complete outer electron shell, making them energetically stable and less inclined to attract additional electrons. However, when an electron is added to a noble gas, it can lead to slight destabilization due to electron-electron repulsion in the resulting anion. As a result, the process of adding an electron is often endothermic, resulting in positive electron affinity values for these elements.