Which group has the most negative electron affinity values?

• A. Halogens; they gain electrons readily to achieve noble-gas configuration
• B. Noble gases; they have full shells
• C. Alkali metals; low electronegativity
• D. Transition metals; high density

Answer: (A)

Electron affinity is the energy change when a neutral atom in the gas phase gains an electron to form an anion; a more negative value means the atom releases more energy in that process. Halogens readily accept an extra electron to complete their octet and achieve a noble-gas configuration, so the gain is highly exothermic and their electron affinities are very negative. In contrast, noble gases resist adding electrons because it would require starting a new shell, giving little to no energy release (often near zero or positive), alkali metals tend to lose electrons rather than gain them, and transition metals show a range of values that are generally not as negative as that of halogens. Therefore, halogens have the most negative electron affinity values.