electron affinity

Question

Which element has the most exothermic (most negative) electron affinity?

RankGuru · Accepted Answer

1. **Definition**: Electron affinity is the energy change when an electron is added to a neutral gaseous atom.
2. **Expected Trend**: Should increase (become more negative) moving up a group ($Cl < F$).
3. **The Discrepancy (F vs Cl)**: 
   - Fluorine is very small. When an electron is added to its $2p$ valence shell, it experiences intense **electron-electron repulsion** from the highly concentrated existing electrons.
   - Chlorine has its valence shell ($3p$) at a greater distance. It is larger, so it can accommodate the extra electron with significantly less repulsion.
4. **Outcome**: Energy released is higher for **Chlorine**. Its electron affinity is the most negative in the periodic table ($-349$ kJ/mol).

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More electron affinity Practice Questions

Which element has the highest electron affinity?