Electron Affinity
Mediumchemistry
Which element has the most exothermic (most negative) electron affinity?
Select the correct option:
Solution
Incorrect! Answer:
Cl
- Definition: Electron affinity is the energy change when an electron is added to a neutral gaseous atom.
- Expected Trend: Should increase (become more negative) moving up a group (Cl<F).
- 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.
- 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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About This Question
- Subject
- chemistry
- Chapter
- classification of elements and periodicity in properties
- Topic
- electron affinity
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Cl
- Definition: Electron affinity is the energy change when an electron is added to a neutral gaseous atom.
- Expected Trend: Should increase (become more negative) moving up a group (Cl<F).
- 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.
- Outcome: Energy released is higher for Chlorine. Its electron affinity is the most negative in the periodic table (−349 kJ/mol).
This medium difficulty chemistry question is from the chapter classification of elements and periodicity in properties, covering the topic of electron affinity. It appeared in the 2025 exam.
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