In FeSO₄, the iron (Fe) atom loses two electrons to form Fe²⁺ cation, while the sulfate (SO₄²⁻) group gains two electrons to form the sulfate anion. The electrostatic attraction between the positively charged iron ions and the negatively charged sulfate ions holds the compound together.

The ionic nature of FeSO₄ can be confirmed by various properties such as its high melting and boiling points, solubility in water, and ability to conduct electricity in the molten state or in aqueous solution.