Nature of C-X Bond in Haloalkane

The C-X bond is polar because halogens are more electronegative than carbon: carbon carries a partial positive charge (delta+) and the halogen a partial negative charge (delta-). The bond forms by overlap of carbon's sp3 orbital with the halogen's half-filled p-orbital. Down the halogen group (F to I) atomic size increases, so C-X bond length increases and bond strength (enthalpy) decreases from C-F to C-I; the table below (measured for CH3X) shows bond length rising and bond enthalpy falling steadily from fluoro- to iodomethane, while dipole moment (bond polarity) actually peaks at CH3Cl rather than CH3F, since polar …