Group 17 - Halogens
Among halogens, which has the weakest X-X bond?
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About This Question
- Subject
- chemistry
- Chapter
- p-block elements
- Topic
- group 17 - halogens
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
F₂
Usually, bond strength decreases as atoms get larger. However, Fluorine (F2) is an anomaly.
- Weak Bond: The F−F bond energy (158.8 kJ/mol) is unexpectedly low, even lower than Cl−Cl and Br−Br.
- Reason: Fluorine atoms are so small that the lone pair-lone pair repulsions between the non-bonding electrons of the two atoms are extremely high. This significantly weakens the single covalent bond.
- Order of bond dissociation enthalpy: Cl2>Br2>F2>I2.
This medium difficulty chemistry question is from the chapter p-block elements, covering the topic of group 17 - halogens. It appeared in the 2025 exam.
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