---
title: "A student studying electron-capture species for a gas-phase detector compares isolated gaseous fluorine and chlorine atoms. Electron affinity is reported as the magnitude of the energy released when one mole of gaseous atoms each gains an electron.  | Atom | Valence configuration before electron addition | Energy released \\(\\text{(kJ/mol)}\\) | |——|———————————————–|————————————–| | \\(\\text{F(g)}\\) | \\(2s^2 2p^5\\) | \\(328\\) | | \\(\\text{Cl(g)}\\) | \\(3s^2 3p^5\\) | \\(349\\) |  Which statement best explains the relative electron affinities of the two atoms?"
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date_modified: "2026-08-19T12:39:45+00:00"
---

# A student studying electron-capture species for a gas-phase detector compares isolated gaseous fluorine and chlorine atoms. Electron affinity is reported as the magnitude of the energy released when one mole of gaseous atoms each gains an electron.

| Atom | Valence configuration before electron addition | Energy released \(\text{(kJ/mol)}\) |
|——|———————————————–|————————————–|
| \(\text{F(g)}\) | \(2s^2 2p^5\) | \(328\) |
| \(\text{Cl(g)}\) | \(3s^2 3p^5\) | \(349\) |

Which statement best explains the relative electron affinities of the two atoms?

A student studying electron-capture species for a gas-phase detector compares isolated gaseous fluorine and chlorine atoms. Electron affinity is reported as the magnitude of the energy released when one mole of gaseous atoms each gains an electron.

| Atom | Valence configuration before electron addition | Energy released \(\text{(kJ/mol)}\) |
|------|-----------------------------------------------|--------------------------------------|
| \(\text{F(g)}\) | \(2s^2 2p^5\) | \(328\) |
| \(\text{Cl(g)}\) | \(3s^2 3p^5\) | \(349\) |

Which statement best explains the relative electron affinities of the two atoms?

- **A.** The electron affinity of \(\text{F(g)}\) is greater because its smaller atomic radius results in a stronger attraction between the nucleus and the added electron.
- **B.** The electron affinity of \(\text{F(g)}\) is greater because its \(2p\) subshell contains fewer electrons before the addition than the \(3p\) subshell of \(\text{Cl(g)}\).
- **C.** The electron affinity of \(\text{Cl(g)}\) is greater because chlorine has fewer occupied energy levels and therefore less electron shielding than fluorine.
- **D.** The electron affinity of \(\text{Cl(g)}\) is greater because the added electron experiences less electron-electron repulsion in chlorine's more spatially extended \(3p\) subshell than in fluorine's compact \(2p\) subshell.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119310/*