Question
Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?
Generally, as we move down the halogen group, the atomic size increases, which leads to longer and weaker bonds, so bond dissociation enthalpy should decrease . However, fluorine () is anomalous. Because of the extremely small size of the fluorine atom, the lone pairs of electrons on the two adjacent bonded atoms experience strong interelectronic repulsions , making the bond weaker than expected. As a result, the bond dissociation enthalpy of is lower than that of both and . According to the standard values , the bond dissociation enthalpies are roughly ( kJ/mol) > ( kJ/mol) > ( kJ/mol) > ( kJ/mol). Therefore, the correct order is .
This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Organic Chemistry – Some Basic Principles and Techniques . Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.
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