Fe3O4 Structure & Characteristics (15 Helpful Facts)

Fe3O4 or iron oxide is the basic oxide having a molecular weight of 231.533 g/mol where Fe shows variable valency. Let us explore more about Fe3O4 in detail.

Fe3O4 is the mixed-valence compound of Fe. Here Fe exists as +2 and +3 oxidation states. In the reaction with water, it gives ferrous hydroxide which is a strong base that’s why it is a basic oxide. In this molecule, no metal-metal bond is present all the Fe are connected with O atoms only with d orbitals.

So, in the hybridization, it formed an inner orbital complex involving the d orbital of Fe and s, and p orbitals of the O atom. Now we can explain the lewis structure, hybridization, bond angle, and other important facts of Fe3O4 with proper explanation in the following part of the article.

1.     How to draw Fe3O4 structure?

The lewis structure of the molecule gives us a clear picture of the covalent characteristics of the molecule. Let us try to draw the lewis structure of Fe3O4 in a few steps.

Counting the valence electrons

1st step of drawing a molecule’s lewis structure is counting the molecule’s total valence electrons by counting the substituents atom. Total valence electrons for the Fe3O4 are 40 which is the contribution of three Fe and four O valence electrons. Here one Fe is in a +2 and the other two +3 oxidation state.

Choosing the central atom

After counting the valence electrons we should choose the central atom for a lewis structure so that we can arrange the other atoms as per requirement. Based on the size and electropositivity Fe is selected as the central atom here, so three Fe are the central atoms and four O are the surrounding atoms.

Satisfying the octet

For every covalent molecule after bond formation, they try to fulfill their octet to gain stability by completing their valence orbitals. For three Fe and four O atoms, the electrons will be required as per octet 7*8 = 56 but the valence electrons for the molecule are 40, so remaining electrons are filled.

Satisfying the valency

Every atom in a molecule is satisfied by its stable valency during the octet. The required 56-40 = 16 electrons should be filled by the 16/2 = 8 bonds and here each Fe and each O are satisfied by their stable valency. Here Fe shows two types of valency, 2 and 3 and O shows only di valency to compete for the bonds.

Assign the lone pairs

The non-bonded electrons after the bond formation exist as lone pairs over the respective atoms. Here O and Fe both contain lone pairs in their respective valence orbitals. To count the total lone pairs we just add the lone pairs of the Fe and O atoms together. The total number of lone pairs is 12.

2.     Fe­­3O4 valence electrons

The valence electrons are present in the outermost shell of each atom involved in the bond formation. Let us count the total valence electrons for the Fe3O4 molecule.

The total valence electrons for the Fe3O4 molecule are 40, involving the valence electrons for the three Fe and four O atoms separately. The valence electrons of Fe are here 5 and 6 respectively. O has six valence electrons as it is a group VIA element. Fe is a d-block element so electrons present in that orbitals are counted.

  • The valence electrons present in the O atoms are 6 (electronic configuration [He]2s22p4)
  • The valence electrons for Fe show +3 oxidation state 5 (3d5)
  • The valence electrons for Fe show +2 oxidation state 6 (3d6)
  • So, the total valence electrons for the Fe3O4 molecule will be 6+(5*2) + (4*6) = 40

3.     Fe3O4 structure lone pairs

The non-bonded electrons present in the outermost orbital after the bond formation are known as lone pairs. Now we count the lone pairs of Fe3O4.

The total lone pairs in the Fe3O4 molecule will be 12 pairs which mean 24 lone pair electrons. Where three Fe atoms and four O atoms’ lone pairs are present. One of Fe contributes two pairs of lone pairs and the other two contribute one pair of lone pairs each. Each O contains for lone pairs separately.

  • The formula to calculate total lone pairs over the Fe3O4 molecule , lone pairs = valence electrons – bonded electrons.
  • The lone pairs over each O atom are, 6-2= 4
  • The lone pairs over Fe having 2 valencies, 6-2 = 4
  • The lone pairs over Fe having 3 valencies, 5-3 = 2
  • So, the total lone pairs over the Fe3O4 molecule will be (4*4) + 4 +(2*2) = 24 lone pairs electrons.

4.     Fe3O4 structure shape

The molecular shape is adopted by the central molecule according to the surrounding environment of other atoms. Let us predict the shape of the Fe3O4.

The molecular shape of the Fe3O4 is tetrahedral around three Fe centers which can be proved from the following table.

No. of
bond pairs
No. of
lone pairs
Shape  Geometry    
AX10Linear  Linear
AX2        20Linear  Linear  
AXE       11Linear  Linear  
AX2E     21BentTrigonal
AXE2     12Linear  Trigonal
AX3E     31Trigonal
AX2E2    2             2BentTetrahedral
AXE3                     13Linear  Tetrahedral
AX4E     41seesawtrigonal
AX3E2    32t-shaped         trigonal
AX2E3    23linear   trigonal
AX5E     51             square
AX4E2                    42square
Fe3O4 Molecular Shape

According to the VSEPR (Valence Shell Electrons Pair Theory), the molecule of AX3E adopted the trigonal pyramidal shape although the geometry will be tetrahedral and the AX2E2 type adopts a bent shape instead of tetrahedral. Here two types of Fe atoms are present due to different oxidation states and adopted both geometries around them.

5.     Fe3O4 structure angle

Bond angle is the angle after adopting a perfect geometry and then making an angle for proper orientation of the atom. let us calculate the bond angle for Fe3O4.

The bond angle for Fe-O-Fe is 109.50 and O-Fe-O is 1040. These two types of bond angles are shown in this molecule because there are two types of Fe center present, and the geometry around them is a different one, is trigonal pyramidal and the other is bent. So, two types of bond angles were observed.

Fe3O4 Bond Angle
  • Let us calculate the bond angle from the hybridization value of the central atom.
  • By using bent’s rule COSθ = (p-1)/p predicts the bond angle
  • For the sd3 hybridization, the s character is 1/4th
  • Then the bond angle will be, COSθ = [(1/4)-1]/(1/4)
  • COSθ = -(1/3)
  • Θ = COS-1-(1/3)
  • Θ = 109.50
  • So, the bond angle will be 109.50 but in bent, geometry is like water and the bond angle decrease to 1040.

6.     Fe3O4 hybridization

The mix of two atomic orbitals to form an equal number of new hybrid orbitals having equivalent energy is called hybridization. Let us explore the hybridization of Fe3O4.

The central Fe in the Fe3O4 is sd3 hybridized here which can be confirmed by the following table.

Structure   Hybridization
State of
of central atom
Bond angle
1.Linear         2         sp /sd / pd1800
3sp2                   1200
3.Tetrahedral 4sd3/ sp3109.50
5sp3d/dsp3900 (axial),
5.Octahedral   6        sp3d2/ d2sp3900
Hybridization Table
  • We can calculate the hybridization by the convention formula, H = 0.5(V+M-C+A),
  • So, the hybridization of central Fe(III) is, ½(5+3+0+0) = 8 (sd3)
  • Again, the hybridization of the other Fe(II) is, ½(6+2+0+0) = 8(sd3)
  • One 4s orbital and three 3d orbitals of Fe are involved in the hybridization.
  • The lone pairs of Fe are also included in the sd3 hybridization.

7.     Is the Fe3O4 solid or gas?

 A molecule is solid or gas depending on the temperature and matter of the state of that particular molecule. Let us see whether Fe3O4 is solid or gas.

Fe3O4 is solid and naturally occurring a black pigment or black power. The main reason to stay solid is that there are many bonds present in the molecule between Fe and O atoms, so the crystal structure of the molecule becomes hard and exists as solid. Both Fe2+ and Fe3+ are present in the solid moiety.

It is extracted from the haematite mineral and different impurities are present in it so it appears black in color in the solid form.

8.     Is Fe3O4 soluble in water?

The solubility in water depends on nature of H bonding and gets dissociated in an aqueous solution at temperature. Let us see whether Fe3O4 is soluble in water or not.

Fe3O4 is insoluble in water at room temperature. It is insoluble in hot and cold water too and the reason is there is a strong bond present within the molecule and the hydration energy of the molecule is very lower than its bond enthalpy, so more energy is required to break the bond and soluble in water.

Although it is a basic oxide so it reacts with water rather soluble in it.

9.     Is Fe3O4 polar or nonpolar

The polarity of a molecule depends on the nonzero resultant t dipole moment and its asymmetrical shape. Let us check whether Fe3O4 is polar or not.

Fe3O4 is a polar molecule and the main reason is the asymmetrical shape of the molecule. The shape of the molecule is bent and trigonal pyramidal around two Fe centers and both the shapes are not symmetrical as there is no chance of canceling the dipole-moment value between Fe to O atoms and making the molecule polar.

Although it is a polar molecule but not soluble in a polar solvent like water so polarity and solubility have no direct relation.

10. Is Fe3O4 a molecular compound?

Molecular compound is those substances made by the proper stoichiometric proportion of the atoms and valency. Let us check whether Fe3O4 is a molecular compound or not.

Fe3O4 is a molecular compound because it is made of three portions of Fe and four portions of O, so the stoichiometric ratio is always fixed for the molecule. Also, their O maintains its di valency and Fe maintains its variable valency like 2 and 3, and there is a proper bond formed between constituent atoms.

If the ratio of Fe and O is changed then it turns to another oxide of iron and no longer will be the Fe3O4.

11. Is Fe3O4 acid or base?

The acidity or basicity depends on the releasing of the H+ and OH in the aqueous solution – Arrhenius theory. Let us see whether Fe3O4 is acid or base.

Fe3O4 is neither acid nor base because it cannot release H+ or OH ions as those ions are absent in this molecule. But it can behave as basic oxide when reacts with water it can form a strong base but itself cannot behave as a base. So, it has an oxide property, not like acid or base.

12. Is Fe3O4 electrolyte?

Substance dissociates in water to break into two ions and carry the electricity through the solution is called electrolytes. Let us see whether Fe3O4 is an electrolyte or not.

Fe3O4 is an electrolyte because it can break into Fe2+, Fe3+, and O2- ions, those ions are highly electrically charged particles and carry electricity through the solution very faster way.  Iron is a d-block metal so it is highly electropositive and O is a highly electronegative atom.  Those ions can make a solution charged by their ionic potential.

13. Is Fe­3O4 salt?

Salts are that substance can form other than H+ and other than OH and are also formed via ionic interaction between them. Let us see whether Fe3O4 is salt or not.

Fe3O4 is a salt because it has cation Fe2+/Fe3+ and anion O2- which differ from H+ and OH. Also, there is somewhat ionic interaction presence because Fe3+ is highly electropositive.  But it cannot be soluble in water although it acts as basic oxide more than salt and due to salt, it has greater bond dissociation energy.

14. Is Fe3O4 ionic or covalent?

No molecule is pure covalent or ionic it is just vice versa according to their polarizability power – Fajan’s rule. Let us check whether Fe3O4 is ionic or covalent.

Fe3O4 is a covalent molecule because the bond present within the molecule Fe and O both share an equal number of electrons in those bonds. Also, the polarity of the bond is not so high that it possesses an ionic character. Although their hybridization occurred in the central atom like a covalent molecule.

The polarizing power of Fe2+ or Fe3+ is not so high that they can polarize the anion. Again, the polarizability of the oxide anion is very poor as it has a smaller size so it shows little ionic character and more covalent character.

15. Is Fe3O4 magnetic?

The magnetic nature of the molecule depends on the presence of the unpaired electrons in the valence shell of the metal. Let us see if Fe3O4 is magnetic or not.

Fe3O4 is a magnetic molecule more specifically it exists as paramagnetic in nature because there are unpaired electrons present in the Fe(III) and Fe(II) centers. As, the oxide is a weakly filed ligand so no paired occurred for the spin, so all the spin of the electrons is the singlet. So, exist as paramagnetic in nature.

  • For the Fe2+ there are four unpaired electrons present and for the Fe3+ five unpaired electrons are present,
  • So, for the Fe3+ center, the paramagnetic nature increases for the molecule.
  •  We can calculate the magnitude of magnetic nature by the formula, [n(n+1]1/2, where n is the number of unpaired electrons.
  • So, the magnitude of Fe2+ is [4(4+1]1/2 = 4.47 B.M.
  • The magnitude for Fe3+ is [5(5+1]1/2 = 5.47 B.M.


Fe3O4 is a mixed-valence molecule of the Fe and it is also a basic oxide that can base reacts with water. It is a normal spinal compound where one metal center adopts tetrahedral geometry and the other adopt octahedral geometry in the lattice structure.

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