Ionization Energy Trend
First ionization energy order (highest to lowest):
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About This Question
- Subject
- chemistry
- Chapter
- classification of elements and periodicity in properties
- Topic
- ionization energy trend
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
Ne > F > N > O
- General Trend: Ionization Energy (IE) generally increases from left to right across a period.
- Noble Gases: Neon (Ne) has a completely filled octet, making it extremely stable. It has the highest IE in its period.
- Halogens: Fluorine (F) is next with a very high effective nuclear charge.
- The Exception (N vs O):
- Nitrogen has a configuration of 1s22s22p3 (half-filled p-subshell). This is inherently stable due to symmetry and exchange energy.
- Oxygen is 1s22s22p4. Removing the 4th electron relieves electron-electron repulsion in the px orbital.
- Result: N has a higher first IE than O.
- Final Order: Ne>F>N>O.
This hard difficulty chemistry question is from the chapter classification of elements and periodicity in properties, covering the topic of ionization energy trend. It appeared in the 2025 exam.
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