KMnO4 Structure & Characteristics (13 Important Facts)


KMnO or potassium permanganate is used for the redox titration having a molecular weight of 158.034 g/mol. Let us discuss KMnO4 in detail.

KMnO4 is a strong oxidizing agent, it can easily be oxidized by many species and undergo self-reduction by the transfer of electrons. The counter anion part is also a strong oxidizing agent, Mn is attached by the four O atoms in a tetrahedral moiety. It is an orthorhombic crystal having purple blackish color.

KMnO4 is mainly used in the titration of oxalic acid as a self-indicator, as it contains characteristics color pink. Now in this article, we have to know the hybridization, lewis structure, bond angle, polarity, and acidity of the KMnO4 with proper explanation.

1.      How to draw the KMnO4 structure?

The lewis structure of any molecule can predict the molecular shape and count the valence electrons. Now we learn how to draw the lewis structure of KMnO4 in a few steps.

Counting the total valence electrons

1st step is counting the total number of valence electrons for any molecule while drawing its lewis structure. The total numbers of valence electrons for the KMnO4 are 32 including the valence electrons of the four O atoms, and one K and Mn atom respectively. We just add them together.

Choosing the central atom

A very important step for drawing the lewis structure of the molecule is choosing the central atoms among all the atoms. The Mn is selected as the central atom for the KMnO4. Because it has a larger size and also it is an electropositive atom so it can hold all the constituent atoms surrounding it.

Satisfying the octet

 In any molecule, we have to check the octet of each atom. In the KmnO4, Mn completed its octet by making bonds with O via sharing electrons. Each O atoms make two bonds with Mn to share two electrons and completed its octet. Even s block element K also shares its electron with O to complete its octet too.

Satisfying the valency

During the bond formation to complete the octet, each atom should be satisfied by its stable valency. Mn has stable valency is 7 and it makes seven bonds with four O atoms. O is made two bonds to satisfy its di valency, and K makes only one bond as it is stable by its mono valency.

Assign the lone pairs

After the required bond is formed among the atom some have more excess electrons in the valence shell. Those electrons exist as lone pairs over that particular atom and participate in the other additional reactions.  In the KMnO4 molecule, only each O contains two pairs of lone pairs.

2.      KMnO4 structure valence electrons

Electrons present in the outermost orbital of atoms are called valence electrons, which are involved in bond formation with other. Now count the valence electrons of KMnO4.

The total number of valence electrons for the KMnO4 molecule is 32 and for K, Mn, and four O atoms the valence electrons together are the same number, so we can say that the valence electrons of the molecule are the summation of the valence electrons of each atom present in that molecule.

  • The valence electrons for the K is 1 (it belongs to the IA group)
  • The valence electrons for the Mn are 7 (belong to the d block element)
  • The valence electrons for each O atom are 6 (belong to group VIA)
  • Now, total valence electrons for the KMnO4 are 1+7+ (4*6) = 32

3.      KMnO4 structure lone pairs

Lone pairs participate in the additional reaction but not in bond formation, present in valence electrons. Let us count the total lone pairs of KMnO4.

There are a total of 8 pairs of lone pairs present over the KMnO4. All the lone pairs are coming from the O site only.  O contains six valence electrons and among them, only two are being used in the bond formation, so the remaining four electrons exist as lone pairs over O. K and Mn have zero lone pairs here.

  • lone pairs are calculated by the formula, lone pairs = number of electrons present in the valence orbital – number of electrons participate in the bond formation.
  • The lone pairs over the Mn is, 7-7 = 0
  • The lone pairs over the K is, 1-1 = 0
  • The lone pairs over each O atom are, 6-2 = 4
  • So, the total lone pairs present over KMnO4, where four O atoms are present, 4*2 = 8 pairs or 16 lone pairs electrons.

4.      KMnO4 structure shape

The shape of the molecule is determined by the proper orientation of the central atom and the surrounding atoms avoid repulsion. Let us predict the shape of the KMnO4.

The shape of the molecule for KMnO4 is tetrahedral which can be shown in the following table.

Molecular
Formula
No. of
bond pairs
No. of
lone pairs
Shape  Geometry    
AX10Linear  Linear
AX2        20Linear  Linear  
AXE       11Linear  Linear  
AX330Trigonal
planar
Trigonal
Planar
AX2E     21BentTrigonal
Planar
AXE2     12Linear  Trigonal
Planar
AX440TetrahedralTetrahedral
AX3E     31Trigonal
pyramidal        
Tetrahedral
AX2E2                2BentTetrahedral
AXE3                     13Linear  Tetrahedral
AX550trigonal
bipyramidal
trigonal
bipyramidal
AX4E     41seesawtrigonal
bipyramidal
AX3E2    32t-shaped         trigonal
bipyramidal
AX2E3    23linear   trigonal
bipyramidal
AX660octahedraloctahedral
AX5E     51             square
pyramidal   
octahedral
AX4E2                    42square
pyramidal 
octahedral
VSEPR Table
KMnO4 Molecular Shape

VSEPR (Valence Shell Electrons Pair Repulsion) theory decides the geometry of the molecule. The AX4 type of molecule has tetrahedral geometry or square planner. But in tetrahedral geometry, there is less steric repulsion than square planner because their bond angle is higher.

5.      KMnO4 structure angle

The bond angle is made by the constituent atoms by proper orientation of them in the adopted geometry. Let us calculate the bond angle for KMnO4.

The perfect bond angle for the KMnO4 tetrahedral molecule is 109.50 according to the VSEPR theory, for the bond angle the tetra coordinated molecule exists without steric repulsion, otherwise, there will be lots of steric crowding coming. To avoid steric repulsion tetrahedral molecule makes that bond angle.

KMnO4 Bond Angle
  • we can also calculate the bond angle value by the hybridization value of the central atom.
  • The bond angle formula according to Bent’s rule is COSθ = s/(s-1).
  • The central atom Mn is sd3 hybridized, so the s character here is 1/4rd
  • So, the bond angle is, COSθ = {(1/4)} / {(1/4)-1} =-( 1/3)
  • Θ = COS-1(-1/3) = 109.50

6.      KMnO4 structure hybridization

The d orbital of Mn and p orbital of O are not compatible for bonding so they undergo hybridization for proper bonding. Let us see the hybridization of KMnO4.

The central Mn atom in the KMnO4 is sd3 hybridized, which can be confirmed by the following table,

Structure   Hybridization
value  
State of
hybridization
of central atom
Bond angle
1.Linear         2         sp /sd / pd1800
2.Planner
trigonal      
3sp2                   1200
3.Tetrahedral 4sd3/ sp3109.50
4.Trigonal
bipyramidal
5sp3d/dsp3900 (axial),
1200(equatorial)
5.Octahedral   6        sp3d2/ d2sp3900
6.Pentagonal
bipyramidal
7sp3d3/d3sp3900,720
Hybridization Table
  • Now we can calculate the hybridization of the Mn by the formula, H = 0.5(V+M-C+A),
  • So, the hybridization of central Mn is, ½(4+4+0+0) = 8 (sd3)
  • One s orbital and three d orbitals of Mn are involved in the hybridization.
  • The double bond and lone pairs are not included in the hybridization.
  • The bond angle value also confirmed the hybridization value of the Mn.

7.      KMnO­­4 solubility

The solubility of KMnO4 depends on the bond dissociation energy between Mn and double-bonded O atoms. Let us check whether it is soluble in water or not.

KMnO4 is soluble in water because it can prone to hydrolysis by the breaking of the Mn and O double bond. The dπ -pπ bonds between O and Mn are not so strong, so they can be broken by the hydration energy and it dissociated into a water molecule. But the solubility of KMnO4 is not so high in water.

Apart from water it can be soluble in,

  • Strong inorganic acid like HCl,
  • An organic non-polar molecule like CCl4 etc.

8.      Is KMnO4 solid or liquid?

The physical state of KMnO4 depends on the strength of the bond and the constituents atoms present in it at a particular temperature. Let us see whether it is solid or not.

KMnO4 is a solid molecule, it appears as a purple-blackish crystalline molecule because there are three double bonds present in the molecule so the molecule is very strong and hard. Also, its lattice structure contains orthorhombic crystal which is very strong in nature, so it exists as a solid.

Although it is solid its hydration energy is more than bond enthalpy and it can be liquified at a higher temperature it can be liquified.

9.      Is KMnO4 polar or nonpolar?

The polarity of the KMnO4 depends on the structure it adopts and also the electronegativity difference between Mn and O. let us see if it is polar or not.

KMnO4 is a polar molecule because it adopts asymmetrical tetrahedral geometry around the central Mn. For this reason, the dipole moment between O to Mn is not canceling out and there is some resultant dipole moment that will be present. Also, the electronegativity difference was observed between O and Mn.

 The bond angle also plays a significant role here in the polarity of the molecule. Due to that bond angle and electronegative difference make the molecule polar.

10. Is KMnO4 acid or base or salt?

For a solid molecule to check its acidity we have to soluble it in water and then check the pH of the solution. Let us see whether KMnO4 is acidic or not.

The aqueous solution of KMnO4 is neither acidic nor basic, it’s neutral because there is no acidic proton or basic OH not present within the molecule, when it is ionized just formed permanganate ion along with potassium cation. Both the ions are neutral in nature based on acidity. So, it is a neutral salt.

It is can behave as salt rather than acid or base but in the solution, it is still neutral in nature.

11. Is KMnO4 electrolyte?

The nature of the substance when it shows electrolytes dissociated into ions carrying electricity through the solution. Let us see whether KMnO4 is an electrolyte or not.

The KMnO4 is a strong electrolyte because it can be dissociated into two highly conductive ions one is K+ and the other is permanganate. Permanganate ions are more stable and highly conductive due to their resonating nature. K+ has higher mobility and higher charge density to carry the electricity in very fast.

12. Is KMnO4 ionic or covalent?

The nature of the bond of the KMnO4 depends on the sharing of electrons and Fajan’s rule of polarizability. Let us see whether it is ionic or covalent.

KMnO4 is a covalent molecule because the bond between them is formed by the hybridization of the central Mn atom and also shares electrons through the hybridization of d and s orbitals. But the bond formed by the O and K by the ionic interaction and the interaction is very strong.

On the other hand, due to rule polarizability, it contains some % of ionic characters also and there will be ionic interaction present potassium ion and permanganate ion.

13. Is KMnO4 an inorganic compound?

A molecule is inorganic it depends on which atoms are present in the molecule whether it is C or other elements. Let us see whether KMnO4 is inorganic or not.

KMnO4 is a pure inorganic compound because it consists of K, Mn, and O atoms only, there is no hydrocarbon part present within the molecule. The hydrocarbon part is made of C and H atoms only and no other element will be present but unlike the KMnO4 there is another element present except C and H.

Not always organic molecule contains C and H only, it contains O, N, S, and halogen as hetero atoms but there must be a hydrocarbon part will be present where C and H make a direct bond.

Conclusion

Potassium permanganate is a strong oxidizing agent and it can be oxidized with much organic functionality, for this reason, it can use in many organic syntheses. It is used in analytical chemistry as a redox titrant and the determination of the strength of oxalic acid KMnO4 is used and it acts as a self-indicator here.

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Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.

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