Which group typically shows the most negative electron affinity values, and why?

• A. Alkali metals; they lose electrons easily
• B. Halogens; they gain electrons readily to achieve a noble-gas configuration
• C. Noble gases; they have full electron shells
• D. Transition metals; they have varied oxidation states

Answer: (B)

Electron affinity is the energy change that occurs when an isolated atom in the gas phase gains an electron. A highly negative value means the atom releases a lot of energy as the new electron is added, indicating a strong drive to achieve a more stable configuration.

Halogens are the group that shows the most negative electron affinities because they are one electron away from a noble-gas configuration. Adding that single electron completes their octet, creating a very stable arrangement, which releases a large amount of energy. Their relatively high effective nuclear charge and small atomic radii also help attract the incoming electron strongly, making the process highly exothermic.

Noble gases have full electron shells, so gaining an electron is not energetically favorable and often requires energy input, giving near-zero or even positive electron affinities. Alkali metals prefer to lose electrons, so gaining one isn’t energetically favorable, leading to small or positive affinities. Transition metals vary a lot due to complex electron configurations, so they don’t exhibit the most negative values on average.