Bond Dissociation Energy Order

$$\text{C--F } (452 \text{ kJ/mol}) > \text{C--Cl } (351 \text{ kJ/mol}) > \text{C--Br } (293 \text{ kJ/mol}) > \text{C--I } (234 \text{ kJ/mol})$$

Concept :

• Orbital Overlap & Bond Strength: Bond dissociation energy is directly proportional to orbital overlap efficiency and inversely proportional to bond length.
• $$\text{C--F}$$ Bond: The 2p orbital of carbon overlaps with the 2p orbital of fluorine ($$2p\text{--}2p$$ overlap), which is exceptionally strong, compact, and short, requiring high energy to cleave.
• $$\text{C--I}$$ Bond: As you move down the halogen group to iodine ($$2p\text{--}5p$$ overlap), the increasing atomic size leads to a longer, diffused bond with poor orbital overlap, making it the weakest bond that breaks most easily.