ACS Chemistry Practice Exam 2026 – The All-in-One Guide to Exam Success!

The group of elements that generally has the highest electron affinity values is the halogens.

Electron affinity refers to the energy change that occurs when an atom in the gas phase gains an electron to form a negative ion. Halogens, located in Group 17 of the periodic table, have significant electron affinity because they are only one electron short of achieving a full valence shell, reaching a stable octet configuration. This drives their strong tendency to gain an additional electron.

In contrast, alkali metals have low electron affinity values because they tend to lose an electron to reach a stable configuration, rather than gain one. Noble gases have virtually zero electron affinity as they already possess a complete octet of valence electrons, making them very stable and unlikely to attract additional electrons. Alkaline earth metals also have lower electron affinity values compared to halogens since they typically lose two electrons to attain a stable electronic configuration rather than gain an electron.

This understanding of electron affinity highlights the variegated nature of element behavior across the periodic table, particularly emphasizing the unique reactivity of the halogens due to their need for just one more electron to complete their valence shell.