Nucleophiles
These are species with lone pairs of electrons, most of the time, negative ions which will be attracted to positive ions or carbocations and they are electron pair donors.
In the picture above, the Chloride ion is a NUCLEOPHILE.
Examples of nucleophiles are the halogen anions (I-, Cl-, Br-), the hydroxide ion (OH-), the cyanide ion (CN-), ammonia (NH3), and water.
Electrophiles
These are species that Accept a pair of electrons to form a new covalent bond
Examples of electrophiles are hydronium ion (H3O+, from Brønsted acids), boron trifluoride (BF3), aluminum chloride (AlCl3), and the halogen molecules fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2).