The molecular formula "FeO2" is a general formula that can represent several chemical compounds: Iron(II) hydroxide, iron oxide and Oxido (oxo) iron. Iron oxide is the most common name for it.
The three compounds that share the molecular formula FeO2 have similar properties and compositions, but retain certain differences. In addition to the molecular formula, the molecular weight and average mass of the compounds are similar, with only Oxido (oxo) iron having a higher molecular weight. Oxido (oxo) iron has a double bond between the iron and one of the oxygen ions. However, the main aspect of the FeO2 is that there are two oxygen ions with an iron ion.