Nature of C-X Bond in Haloarenes

In a haloarene, the ring carbon bonded to the halogen is sp2 hybridised; sp2 orbitals are shorter and hold the bonding electron pair more tightly than sp3 orbitals do. Also, one of the halogen's lone pairs, sitting in a p-orbital, conjugates with the ring's pi system, forming an extended, delocalised system -- shown by the resonance structures placing a positive charge on the halogen and pushing extra electron density (and formal negative charge) onto the ring's ortho/para carbons. This partial delocalisation gives the C-X bond in a haloarene double-bond character, making it both shorter and stronger than the C-X bond of a haloalkane. Measured example: the C-Cl bon …