Bond Length

$$\text{Bond Length Order: } \text{C--I} > \text{C--Br} > \text{C--Cl} > \text{C--F}$$

$$\text{Bond Dissociation Energy (BDE) Order: } \text{C--F} > \text{C--Cl} > \text{C--Br} > \text{C--I}$$

Concept & Explanation:

• Bond Length: As you move down the group from fluorine to iodine ($$\text{F} \to \text{Cl} \to \text{Br} \to \text{I}$$), the atomic size of the halogen increases significantly. Larger halogen atoms result in greater inter-nuclear distance, making the $$\text{C--I}$$ bond the longest and $$\text{C--F}$$ the shortest.
• Bond Dissociation Energy: Bond strength is inversely proportional to bond length. Because the $$\text{C--F}$$ bond is extremely short and has strong orbital overlap ($$2p\text{--}2p$$), it requires the highest energy to break. Conversely, the long $$\text{C--I}$$ bond ($$2p\text{--}5p$$) is weak and breaks most easily.