FeO

Iron(II) oxide

Names
IUPAC name Iron(II) oxide
Other names Ferrous oxide,iron monoxide
Identifiers
CAS Number	1345-25-1 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:50820 Y
ChemSpider	14237 Y
ECHA InfoCard	100.014.292
Gmelin Reference	13590
PubChem	14945
UNII	G7036X8B5H Y
InChI InChI=1S/Fe.O Y Key: UQSXHKLRYXJYBZ-UHFFFAOYSA-N Y InChI=1/Fe.O/rFeO/c1-2 Key: UQSXHKLRYXJYBZ-WPTVXXAFAB
SMILES [Fe]=O
Properties
Chemical formula	FeO
Molar mass	71.844 g/mol
Appearance	black crystals
Density	5.745 g/cm3
Melting point	1,377 °C (2,511 °F; 1,650 K)
Boiling point	3,414 °C (6,177 °F; 3,687 K)
Solubility in water	Insoluble
Solubility	insoluble in alkali, alcohol dissolves in acid
Magnetic susceptibility (χ)	+7200·10−6 cm3/mol
Refractive index (nD)	2.23
Hazards
Main hazards	can be pyrophoric
Safety data sheet	ICSC 0793
NFPA 704	0 0
Autoignition temperature	variable
Related compounds
Other anions	iron(II) fluoride, iron(II) sulfide, iron(II) selenide, iron(II) telluride
Other cations	manganese(II) oxide, cobalt(II) oxide
Related compounds	Iron(III) oxide, Iron(II,III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, which consists of hydrated iron(III) oxide (ferric oxide). Iron(II) oxide also refers to a family of related non-stoichiometric compounds, which are typically iron deficient with compositions ranging from Fe_0.84O to Fe_0.95O.

FeO can be prepared by the thermal decomposition of iron(II) oxalate.

The procedure is conducted under an inert atmosphere to avoid the formation of ferric oxide. A similar procedure can also be used for the synthesis of manganous oxide and stannous oxide.

Stoichiometric FeO can be prepared by heating Fe_0.95O with metallic iron at 770 °C and 36 kbar.

FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe₃O₄:

Iron(II) oxide adopts the cubic, rock salt structure, where iron atoms are octahedrally coordinated by oxygen atoms and the oxygen atoms octahedrally coordinated by iron atoms. The non-stoichiometry occurs because of the ease of oxidation of Fe^II to Fe^III effectively replacing a small portion of Fe^II with two thirds their number of Fe^III, which take up tetrahedral positions in the close packed oxide lattice.

Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.

Iron(II) oxide makes up approximately 9% of the Earth's mantle. Within the mantle, it may be electrically conductive, which is a possible explanation for perturbations in Earth's rotation not accounted for by accepted models of the mantle's properties.