Which statement about electron affinity and periodic trends across a period is accurate?

• A. Electron affinity is the energy required to remove an electron.
• B. Electron affinity is the energy change when an atom gains an electron but is generally exothermic across a period.
• C. Electron affinity is the energy change when an atom gains an electron; noble gases have very high affinity compared with other elements.
• D. Electron affinity is the energy change when an atom gains an electron; generally becomes more negative across a period as nuclear charge increases; noble gases have very low or endothermic values; exceptions exist.

Answer: (D)

Electron affinity is the energy change when an atom gains an electron. Across a period, the increasing nuclear charge pulls added electrons in more strongly, so the energy released (the magnitude of the affinity) tends to become more negative as you move from left to right. Noble gases, with closed shells, don’t readily accept electrons, so their affinities are very small or even endothermic. There are occasional anomalies due to how electrons pair in subshells and repulsion effects, but the overall pattern is a general shift toward more negative values across a period, with noble gases standing out as the exception. That combination—energy change for gaining an electron, trending toward more negative values across the period, and very low or endothermic values for noble gases—matches the statement best.