89104b46_onds_vs_Ionic_Bonds___Chemwiki__Ionic_Bonds
[0] Formation: [Covalent Bonds] A covalent bond is formed between two non-metals that have similar electronegativities. Neither atom is "strong" enough to attract electrons from the other. For stabilization, they share their electrons from outer molecular orbit with others [Ionic Bonds] 
An ionic bond is formed between a metal and a non-metal. Non-metals(-ve ion) are "stronger" than the metal(+ve ion) and can get electrons very easily from the metal. These two opposite ions attract each other and form the ionic bond.
Covalent Bonds vs Ionic Bonds - Chemwiki
Ionic Bonds