I3- or triiodide ion is a polyatomic molecule or a charged molecule having actually a net an adverse charge that -1.

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I2 + I- —-> I3-

This is the exergonic equilibrium resulting in the development of the ion whereby a positive circulation of energy happens indigenous the device to the surroundings.

One of the major uses the this ion is due to its non-reactive residential or commercial property with starch which outcomes in an identifiable blue-black color used a lot for identification.

It is a major component that a many salts.

Now, permit us discover the interior chemistry and also make ourselves aware of its bonding nature in order come gain an ext insight right into its properties.

Lewis framework of I3

Anyone wanting to recognize in-depth around a molecule demands to learn around the Lewis Structure. Why is it so crucial to have actually an idea ~ above this topic?

Well, Lewis framework is the name provided to the diagrammatic depiction of chemical bonding developing between atoms inside a molecule.

Also well-known as Lewis electron period structures, the is based top top the octet rule of valence electrons.

It is a vital concept to know the characteristics and hybridization that a molecule because it help us attract the chemical structure.

To uncover out the Lewis framework of I3, allow us inspect all the actions in the complying with process.

Step 1

At the an extremely beginning, we should calculate the complete valence electron number.

While act so, we have to attend to two signs: the hopeful or the ‘+’ sign and also the an unfavorable or the ‘-’ sign.

The an initial one means electron loss while the last signifies the absorbing or get of negatively fee electrons thus increasing the an adverse charge that the molecule.

Step 2

After we have measured the total number of valence electrons, we have to discover out which one is the main atom.

In bespeak to execute so, we require to check the atom having the highest possible valence i.e. The the very least electronegative one. This main atom is walking to have actually a larger variety of bonding sites with respect to the other elements.

Step 3

The third step is based upon sketching the skeleton diagram of the offered molecule. This is excellent to visualize the solitary bonds in the positions that they room present.

Step 4

Most of you are currently familiar v the term ‘octet rule’. It is basically a thumb dominance that claims that every atom of a molecule requirements to have eight valence electron (electron count in the outermost shell).

So, ours duty right here is to do the octet completion. Because that your very own ease, try to begin with the electropositive ones first.

Step 5

After we have actually completed octets the atoms approximately other atoms, we must verify whether more bonds are needed to it is in formed.

Double binding or if crucial triple bond are hence formed.

Step 6

We are now done through all kinds of shortcut formation, The last step is focused on the formal charge concept.

If we have the right to confirm that all the atoms inside a given molecule are preserving their officially charges at their lowest value, our Lewis framework is complete.

Calculation of formal fee is done by simply complying with this easy formula.


For I3 (Triiodide ion)

1. I3 is composed of 3 iodine present in that molecule. The atomic number is 53 and also it consists of 7 electron in the outermost shell.

We likewise have an additional electron to provide the overall an unfavorable charge to the I3 molecule.

Total variety of valence electrons = 3*7+ 1=21 + 1=22

2. Since all the atoms are iodine, one of these theatre the role of the central atom.


3. Together you deserve to see in the above diagram, the skeletal structure of I3 through the an adverse charge has been drawn.

4. This step is pertained to with the octet dominion fulfillment.

According to the octet rule, the greatest multiple of 8 under the full no. Of valence electrons (step1) requirements to it is in considered. Here, the worth is 16. Now, 22-16=6.

Hence, the iodine atom at the facility in between the various other two atoms is going to have 3 lone pairs(6) electrons v itself.

Forming the solitary bonds with the various other two iodine, we uncover out the there are 3 lone pairs and also 2 link pairs for the main iodine.

5. Check the formal charge, we put the an unfavorable charge outside as per the diagram above.Thus, lewis framework is done.

Hybridization that I3

The hybridization that I3 (Triiodide ion) is sp3d.

The way we attract the framework of molecule compounds on document is just a two-dimensional form.

The expertise of chemistry reactions and physical properties can be better understood with the image in a 3-dimensional platform.

And, this image of the orientation of atoms inside any simple or facility compound is based upon the hybridization concept.

A an easy formula to examine out the hybridization number is:


Where, C= fee of cations; A=charge the anions, V= the total variety of valence electrons, M= Monovalent atoms and H stands for the ultimate hybridization value.

Here, in the case of -, 2 monovalent atoms room present, for this reason M=2, seven valence electrons space there, V=7, A=1, and C=0.

therefore, H= 5

As per knowledge, since sp hybridization worth is 2, an in similar way we can discover out the for H=5, the type is sp3d.

Molecular Geometry that I3

If us take one more look at the Lewis structure of the ion I3-, us can easily see that the main iodine has three lone pairs.

The lone pairs space positioned equatorially due to repulsion.

Hence, the other two iodine atom are placed axially and also the bond angle made is 1800.

If us have focused on the formal fee theory, we know that that is the central atom that has the negative charge, therefore the donor.

The form of the I3- ion, therefore, is linear and symmetrical.



I3- is an exciting and challenging molecule to deal with when it pertains to chemical bonding.

Although the molecular geometry is linear as debated earlier, the digital geometry is trigonal bipyramidal.The framework of triiodide ions is such the the center atom carries the ‘-’ charge.

Now, as we talk about polarity, allow us define it.

In chemistry, polarity means something that will certainly bear a non-zero worth of dipole moment.

Dipole moment, thus, is a measure of polarity and is a result of electronegativity difference inside a molecule.

It usually developed due to the separation of confident and an unfavorable charges and also depends on the distance between them.

Here, if we examine I3- has actually a an unfavorable charge but also it is symmetrical in molecule geometry through no resultant dipole moment. Instead, the complete charge that the molecule is an adverse as deciphered earlier.

So, even if it is to contact this triiodide ion a polar or nonpolar molecule is a subject of debate but if we look at the solubility factor, we can infer the it is polar( I3- is dissolve in water).

I3 MO (Molecular Orbital) Diagram

Triiodide ion is a shining example of 3-center-4-electron chemistry bonding.

Now, what does it signify?


Before that, a brief summary of MO or molecule Orbital theory is placed prior to you.

Now, as many of us room aware, a molecular orbit is a duty to recognize the location and also wave-like nature, thus, a delocalized method to bonding.

A MO deserve to have a best of 2 electrons. MO outcomes from overlapping in between AO(atomic orbitals) the the same energy.

In the case of I3-, the no. That valence electrons is 22. An atom that iodine has actually the valence orbitals in the below fashion:5s, 5px, 5py, 5pz

5s and also 5px, 5py are low in energy and weak, as such non-bonding. 5pz is left yet it has actually both bonding and a non-bonding lone pair, the last one positioned ~ above the side iodine atoms providing them each a -0.5 officially charge.

Together, the 10 non-bonding pairs and one single bond offers 22 valence electrons as calculated earlier.


Triiodide ion is certainly one the the most advantageous topics of chemical bonding due to its tricky nature and important features.

Here, we had a sneak peek into the hybridization, Lewis Structure, Polarity, Shape, and Orbital concept.

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This certain will help you recognize the physical and chemical nature of compounds having I3- in a better fashion.