Iron(II) oxide or ferrous oxide is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the formula FeO. Its mineral form is known as

wüstite Wüstite ( Fe O) is a mineral form of iron(II) oxide found with meteorites and native iron. It has a grey colour with a greenish tint in reflected light. Wüstite crystallizes in the isometric-hexoctahedral crystal system in opaque to translu ...

. One of several

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of wh ...

s, it is a black-colored powder that is sometimes confused with

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

, the latter of which consists of hydrated

iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally a ...

(ferric oxide). Iron(II) oxide also refers to a family of related

non-stoichiometric compound In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); m ...

s, which are typically iron deficient with compositions ranging from Fe_0.84O to Fe_0.95O.

Preparation

FeO can be prepared by the thermal decomposition of iron(II) oxalate. :FeC₂O₄ → FeO + CO₂ + CO The procedure is conducted under an inert atmosphere to avoid the formation of

(Fe₂O₃). A similar procedure can also be used for the synthesis of manganous oxide and

stannous oxide Tin(II) oxide (stannous oxide) is a compound with the formula SnO. It is composed of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form. Preparation and reactions Bl ...

. Stoichiometric FeO can be prepared by heating Fe_0.95O with metallic iron at 770 °C and 36 kbar.Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford University Press

Reactions

FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe₃O₄: :4FeO → Fe + Fe₃O₄

Structure

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. In contrast to the crystalline solid, in the molten state iron atoms are coordinated by predominantly 4 or 5 oxygen atoms. Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.

Occurrence in nature

Iron(II) oxide makes up approximately 9% of the Earth's

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

. 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.

Uses

Iron(II) oxide is used as a

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

. It is FDA-approved for use in cosmetics and it is used in some

tattoo A tattoo is a form of body modification made by inserting tattoo ink, dyes, and/or pigments, either indelible or temporary, into the dermis layer of the skin to form a design. Tattoo artists create these designs using several tattooing ...

inks. It can also be used as a phosphate remover from home aquaria.

References

External links

Wustite Mineral Data
{{oxygen compounds Iron(II) compounds Iron oxide pigments Non-stoichiometric compounds Transition metal oxides Rock salt crystal structure Glass dyes