An ionic bond is a type of chemical bond established between two atoms by the transfer of the valence electrons from one atom to another. This type of bond is also known as electrovalent or polar bond. Salts are a good example of substances made with ionic bonding.
An ionic bond involves a metal and a nonmetal atom. Every atom has a tendency to achieve the stable electron configuration, which means achieving the octet number (2 or 8) to its valance shell. The metal atom has excess electrons above the octet number in its valance shell. On the other hand, the nonmetal atom is short of electrons and hence needs electrons to fulfill its octet. Once they come to each other, the metal atom surrenders its surplus electrons to the nonmetal atom. As a result of this electron transfer, each of the atoms attains the stable electron configuration. The compound is formed by this bond called ionic or electrovalent compound. In ionic bonds, the net charge of the compound must be zero. Some examples of ionic compounds are: NaCl (sodium chloride), MgO (magnesium oxide), CaF2 (calcium fluoride) and Al2O2 (aluminum oxide). In the real world, compounds with pure ionic bonding are not known to exist. All ionic compounds have a degree of covalent bonding.