Explanation
Ionic bonding generally occurs between a metal and a non metal atom. The metal has a tendency to lose electrons and become positively charged. The resulting positive ion is called a cation. The non metal has a tendency to gain electrons and become negatively charged. The negative ion is called an anion. The electrostatic force of attraction between these oppositely charged ions is defined as ionic bond.
Example
Sodium (metal) has an electronic configuration of 2,8,1. It needs to lose one electron to achieve noble gas configuration and fulfil octet rule. Chlorine (non metal) has an electronic configuration of 2,8,7. It needs to gain one electron to fulfil octet rule. This transfer of electron between the atoms results in an ionic bond between them as shown below.
2,8,1 2,8
2,8,7 2,8,8
