Large ionic compound crystals: blue - copper sulphate: white - potassium aluminium sulphate

Large ionic compound crystals: blue - copper sulphate: white - potassium aluminium sulphate also called alum.

When a metal bonds with a non metal an electron is transferred. This transfer bonds them closely together.

KAl (SO4)2 is ionic. It contains K+, Al3+ and SO42- ions. The sulfate ions contain covalent bonds. It is normally encountered as the dodecahydrate (12 water molecules), KAl(SO4)2.12H2O and is called potassium alum or more often just alum.

Copper sulfate has both kinds of bonding: Copper cations and sulfate anions are held together by ionic bonding, and the sulfate ions are maintained as entities by covalent bonds.