f.4 chem,,,,ionic bonding

it's because metal atoms will lose electrons to form cations with positive charges and non-metal atoms will gain the electrons from the metal atoms to form anions with negative charges. Ionic bond presents between metal atoms and non-metal atoms only because, they will only form cations and anions respectively and combine to be a compound.
For example, in metallic bond and covalent bond, there are no cations and anions present. Because in metallic bond, the electrons are delocalized and move from one atom to another. In covalent bond, the atoms will share the electrons to get an octet structure.
In short, ionic bond a bond formed by the attraction between two oppositely charged ions.

There have one special case,NH4+ ION,CAN U EXPLAIN IT?