Which group of elements in the periodic table absorbs the most energy (has the least negative electron affinity) when gaining an electron?

• A. Alkali metals (Group 1)
• B. Halogens (Group 17)
• C. Alkaline earth metals (Group 2)
• D. Noble gases (Group 18)

Answer: (D)

Verified step by step guidance

1. Understand the concept of electron affinity: Electron affinity is the energy change that occurs when an atom gains an electron. A more negative electron affinity means the atom releases energy and more readily gains an electron, while a less negative (or positive) electron affinity means the atom absorbs energy and is less likely to gain an electron.
2. Recall the general trends in electron affinity across the periodic table: Electron affinity tends to become more negative (more energy released) as you move from left to right across a period, because atoms more strongly attract additional electrons to complete their valence shells.
3. Consider the groups given: Alkali metals (Group 1) have a single valence electron and tend to lose electrons rather than gain them, so their electron affinities are relatively low in magnitude. Halogens (Group 17) are one electron short of a full valence shell and have highly negative electron affinities, meaning they release a lot of energy when gaining an electron. Alkaline earth metals (Group 2) have filled s subshells and generally have low electron affinities.
4. Focus on the noble gases (Group 18): They have full valence shells, making them very stable. Adding an electron requires placing it in a new, higher energy orbital, which is energetically unfavorable. Therefore, noble gases have positive or very low (least negative) electron affinities, meaning they absorb energy when gaining an electron.
5. Conclude that the group with the least negative electron affinity (absorbing the most energy) when gaining an electron is the noble gases (Group 18), because their full valence shells make electron addition energetically unfavorable.