As a general rule, a molecule cannot belong to both categories. Before going into detail, it is important to clarify that the etymology of these terms must be understood in order to better assimilate the information. In short, the term "electro" refers to electrons, "nucleo" refers to the nucleus, and "philia" comes from the Greek philos meaning the idea of loving/being attracted to. Now, keep this information in mind and let's see what these terms used mainly in chemistry are.
Electrophiles are atoms or molecules that are known to be electron deficient and carry a partial or full positive charge. These molecules aim to create covalent bonds with nucleophiles in order to acquire an electron pair.
Because of their electron deficiency, electrophilic molecules are characterized by a particular attraction to electrons. This deficiency therefore grants the necessary characteristics to electrophiles to be part of the category of Lewis acids.
Unlike the electrophile, nucleophiles are molecules that will present an attraction to the nucleus (nuclei). Being part of the category of Lewis bases, the attraction of nucleophiles to nuclei is justified by the principle of chemistry which states that opposites attract. Since nuclei are charged with protons, which have positive charges, nucleophiles are attracted to them to go and make bonds. To do this, nucleophiles give a pair of electrons to electrophilic molecules and thus access the nucleus.
Obviously, the principle of this categorization is much more complex than just that. Some molecules may have a nucleophilic part and an electrophile. However, since the goal is to understand the difference between these two categories, we will recall only that:
- The electrophile seeks to create covalent bonds with the nucleophiles in order to receive a pair of electrons
- The nucleophile is attracted by the prominence of the nucleus in the electrophile and wants to share its electrons to create bonds.
The exchange of electrons between these molecules causes chemical reactions allowing the creation of chemical compounds different from the original ones. In other words, the differences of these bases and acids cause the reactions between the different chemical compounds.