Which statement best describes the electron affinity of noble gases?

• A. Noble gases have very low or endothermic electron affinity values.
• B. Noble gases have highly exothermic electron affinities.
• C. Noble gases readily gain electrons to form anions.
• D. Noble gases have electron affinity equal to halogens.

Answer: (A)

Electron affinity is the energy change when a neutral atom in the gas phase gains an extra electron. Noble gases have full outer electron shells, which makes them very stable and largely unwilling to accept another electron. Adding an electron to a closed shell involves placing it into a higher energy situation and increasing electron-electron repulsion, so little energy is released and the process is not favorable. In many cases it is slightly endothermic, or effectively zero, which is why noble gases show very low electron affinities. This is in contrast to halogens, which release energy when they gain an electron and form stable anions.