Dative Covalent Bonding

Picture from Google pic 

It's also called as Co-ordinate bonding. It's formed when an atom provides both electron for covalent bonding. 

- One atom have a lone pair electron, to provide both electron

- One atom that lacks electron, to accept the lone pair of the other atom

The picture above shows exactly how the dative covalent bonding is processed and looks like. As N have 5 electrons and only bonded to 3 electrons, it act as a donor and bonded to the hydrogen ion who lakes of electron. The arrow from nitrate to hydrogen on the right side shows the coordinate bond and that nitrate is the one who provide the both electron needed for the bonding. As hydrogen ion is already become one with the ammonia molecule, and ammonia molecule have nothing to cancel out the charge, therefore the charge is still following the hydrogen ion.