Bond Polarity

Halogens are more electronegative than carbon, so the carbon-halogen bond in a halogenoalkane is a polar bond. The halogen atom pulls the bonding pair of electrons towards itself and gains a partial negative charge (δ-), leaving the carbon atom with a partial positive charge (δ+).Electronegativity decreases down group 7, so the polarity of the bond decreases in the order C-F > C-Cl > C-Br > C-I. The C-I bond is only very slightly polar because iodine and carbon have similar electronegativities.The δ+ carbon atom is electron deficient. This makes it open to attack by nucleophiles, which are electron pair donors attracted to the partially positive carbon atom.The polar bond also gives halogenoalkane molecules permanent dipole-dipole forces between them, in addition to van der Waals forces.