The word ‘phile’ comes from Greek and means ‘loving’. A nucleophile is therefore ‘nucleus loving’. We know that a nucleus is positively charged as it contains protons and neutrons. A species which is ‘nucleus loving’ would therefore be negatively charged or contain electrons for bonding, as it is attracted to the nucleus. Hence, nucleophiles are species that can donate electrons, and can therefore be classified as Lewis bases. Some examples are H2O (oxygen has 2 lone pairs of electrons) and -O-CH3 (negatively charged).
An electrophile is ‘electron loving’. A species which is ‘electron loving’ would be positively charged as it is attracted towards electrons. Thus, electrophiles are either positively charged or have the ability to accept a lone pair of electrons (empty orbitals) and are attracted to an electron rich species. Since they can accept electron pairs, they are also classified as Lewis acids. Some examples include H+ (positively charged) and AlCl3 (Al has a vacant orbital to accept electrons).
Nucleophiles: electron rich
Electrophiles: electron deficient