A nucleophile is an electron pair donor. It has a lone pair of electrons that it can donate to form a new dative covalent bond.Nucleophiles are electron-rich. They are either negatively charged ions, such as OH- and CN-, or neutral molecules with a lone pair, such as NH3 and H2O.Nucleophiles attack atoms that are electron deficient, such as positive ions or the δ+ carbon in a polar bond.For example, the δ+ carbon in the C-X bond of a halogenoalkane is attacked in nucleophilic substitution, and the δ+ carbon in the C=O group of a carbonyl compound is attacked in nucleophilic addition.