Ferrous Oxide(FeO) Properties(25 Facts You Should Know)

Ferrous oxide (FeO) is an inorganic compound. Let us study some facts about ferrous oxide.

Ferrous oxide is a black crystalline inorganic compound found in the mineral wüstite. About 9% of the earth’s mantle is made up of ferrous oxide. It gets easily oxidized in air to give ferric oxide, in which the oxidation state of iron is +3. FeO is mainly used as a pigment and as a polishing agent for glazing pottery.

In this article, some important facts and properties of Ferrous oxide, such as IUPAC name, color, density, structure, and reaction with acids are discussed.

Ferrous Oxide IUPAC Name

The IUPAC (International Union of Pure and Applied Chemistry) of ferrous oxide is Iron (II) oxide.

Ferrous Oxide Chemical Formula

Ferrous oxide has the chemical formula FeO.

Ferrous Oxide CAS Number

The CAS number (authentic numeric identifier which can contain upto10 digits) of ferrous oxide is 1345-25-1.

Ferrous Oxide Chemspider ID

The ChemSpider ID (ChemSpider is a free chemical structure database) for ferrous oxide is 14237.

Ferrous Oxide Chemical Classification

Ferrous oxide is an inorganic non-stoichiometric compound, more precisely written as Fe0.95O.

Ferrous Oxide Molar Mass

The molar mass (mass of one mole of a substance) of ferrous oxide is 71.8444 g/mol.

Ferrous Oxide Color

Ferrous oxide is a dry black-colored powder.

Ferrous Oxide Molar Density

The molar density of ferrous oxide is 0.07996 mol/cm3, and the density of ferrous oxide is 5.745 g/cm3.

Ferrous Oxide Melting Point

The melting point of ferrous oxide is 1377 °C (1650 K) or 2511 °F.

Ferrous Oxide Boiling Point

The boiling point of ferrous oxide is 3414 °C (3687 K) or 6177 °F.

Ferrous Oxide State at Room Temperature

At room temperature, the ferrous oxide is a solid black-colored compound.

Ferrous Oxide Ionic Bond

An ionic bond is a linkage between two atoms due to the electrostatic attraction of opposite charges. In FeO, an ionic bond is formed due to the difference in electronegativity between Fe and O.

Ferrous Oxide Ionic Radius

The ionic radius of cation Fe2+ 0.077 nm and that of the anion O2- is 0.140 nm. Hence, FeO has an ionic radius of 0.217 nm.

rcationranionrcation + ranion = rionic radii
The ionic radius of FeO

Ferrous Oxide Electron Configurations

Electronic configurations show how the electrons are distributed in atomic orbitals. Let us see the electronic configuration of FeO.

  • Electronic configuration of Fe: 1s2 2s2 2p6 3d6 4s2.
  • Electronic configuration of divalent iron (Fe2+): 1s2 2s2 2p6 3d6.
  • Electronic configuration of O: 1s2 2s2 2p4. 
  • Electronic configuration of oxide (O2-): 1s2 2s2 2p6.

Ferrous Oxide Oxidation State

The oxidation state of iron in ferrous oxide is +2 as it donates two electrons from its last shell to oxygen.

Ferrous Oxide Alkaline

Ferrous oxide is a metallic oxide and oxides of transition metals (like Fe) are basic in nature, especially when the metal is in its lower oxidation state. Fe in FeO exhibits a lower oxidation state of +2 and hence is basic.

Is Ferrous Oxide Odourless?

Ferrous oxide is odourless.

Is Ferrous Oxide Paramagnetic?

Paramagnetism arises due to the presence of unpaired electrons, and a magnetic field attracts such substances. Let us analyze whether FeO is paramagnetic or not.

Ferrous oxide is paramagnetic with a magnetic moment of 4.89 BM, since Fe2+ has one paired and four unpaired electrons in its 3d orbital.

Ferrous Oxide Hydrates

Ferrous oxide does not form hydrates as it does not dissociate into ions in water.

Ferrous Oxide Crystal structure

Ferrous oxide has a cubic lattice rock salt type structure (FCC). The ferrous ions are present in octahedral voids, i.e., at the unit cell’s body center and edge center. The corners and faces of the cube are occupied by oxide ions.

Image1 1
FeO structure

Ferrous Oxide Polarity and Conductivity

  • The nature of the bond in FeO is polar covalent. Bond polarity depends upon the difference in electronegativity of the atoms. The electronegativity (EN) of oxygen and iron are 3.4 and 1.8 respectively, and the EN difference is 1.6.
  • Ferrous oxide is a bad conductor of electricity due to the poor dissociation of ions in water.

Ferrous Oxide Reaction With Acid

Ferrous oxide reacts with hydrochloric acid and produces ferrous chloride and water. FeO dissolves in sulphuric acid to form ferric sulphate (Iron (III) sulphate). With nitric acid, Iron (II) oxide produces Iron (III) nitrate or ferric nitrate.

  • FeO + 2HCl FeCl2 + H2O.
  • 2FeO + 4H2SO4  Fe2(SO4)3 +4H2O + SO2.
  • 3FeO + 10HNO3  5H2O + NO + 3Fe(NO3)3.

Ferrous Oxide Reaction With Base

Ferrous oxide is a basic metal oxide that does not react with other bases.

Ferrous Oxide Reaction With Oxide

Ferrous oxide gets readily oxidized with exposure to air and produces ferric oxide.

4FeO + O2  2Fe2O3

Ferrous Oxide Reaction With Metal

Ferrous oxide is thermodynamically unstable and tends to undergo disproportionation to Fe and Fe3O4.


Ferrous oxide is Iron (II) oxide or FeO is an oxide of iron. There are two other oxides of iron in existence, which are Iron (III) oxide (Fe2O3) and Iron (II, III) oxide (Fe3O4). FeO is an electrovalent (ionic) compound, exhibiting a cubic structure. Ferrous oxide is hazardous when its dust is inhaled as it causes nasal and throat irritation.