To begin, it is important to note that each of these three types of bonding is very strong.

Both ionic and metallic bonding rely on electrostatic forces of attraction between oppositely charged particles. In ionic compounds this is the attraction between oppositely charged ions, meanwhile in metals it is the attraction between positively charged metal ions and a sea of delocalised electrons. These "free" electrons give metals the properties of malleability and electrical conductivity. 

Covalently bonded molecules share a pair of electrons in a bond. Though their intra-molecular bonding is very strong, simple covalent molecules are attracted to each other by relatively weaker intermolecular forces known as Van der Waals. forces