2FeO

2FeO is a chemical formula that represents two formula units of iron(II) oxide, also known as ferrous oxide. Iron(II) oxide is an inorganic compound with the chemical formula FeO. It is a black solid that is stoichiometrically impure and is often represented by the empirical formula FeO because of defects in its crystal structure. The actual composition can vary, with iron content typically ranging from 77.7% to 77.9% by weight. This deviation from the ideal stoichiometry is due to the presence of vacancies in the iron sublattice.

FeO crystallizes in the rock-salt crystal structure, similar to magnesium oxide, where iron cations occupy octahedral holes in a face-centered cubic lattice of oxide anions. However, due to the presence of vacancies, the true structure is more complex. At high temperatures, FeO is thermodynamically stable, but it disproportionates into metallic iron and iron(III) oxide (Fe3O4) below 575 degrees Celsius.

Iron(II) oxide is an important component in various industrial processes, including the production of steel. It is also found naturally in some minerals and can be formed through the partial oxidation of iron. Its magnetic properties are also of interest.