Heterolytic fission of the molecules containing covalent bond results in two entities;   one electron deficient, called electrophiles and other electron rich, called neutrophiles.

Electrophiles:

Atoms or group of atoms which are able to attacked electrons is called electrophiles. In short, electrophiles are 'electron loving' groups.
Fig:

ELECTROPHILIC ADDITION

The electrophiles are electron deficient species and can accept a pair of electrons.They usually carry  positive charge and are generally represented by E+ . Some common example of electrophiles are :H+, NO2+ etc.
 There are some electrophiles which are neutral. Lewis acids like:-AlCl3, BF3, SO3, etc.

Neutrophiles:

  
Atoms for group of atoms which are able to be attached   towards electron deficient centre are called neutrophiles.Thus neutrophiles are electron rich species. The neutrophiles may be called as 'nucleus loving' groups. The neutrophiles usually carry negative charge.