I3- or triiodide ion is a polyatomic molecule or a fee molecule having actually a net negative charge that -1.

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I2 + I- —-> I3-

This is the exergonic equilibrium bring about the formation of the ion whereby a positive flow of power happens from the device to the surroundings.

One the the significant uses of this ion is as result of its non-reactive building with starch which outcomes in an identifiable blue-black shade used a lot for identification.

It is a significant component of a many salts.

Now, let us find out the inner chemistry and also make ourselves conscious of that is bonding nature in order to gain more insight into its properties.

Lewis framework of I3

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

Well, Lewis structure is the name provided to the diagrammatic representation of chemical bonding occurring between atoms within a molecule.

Also known as Lewis electron period structures, the is based ~ above the octet ascendancy of valence electrons.

It is a an essential concept to know the characteristics and hybridization the a molecule since it help us attract the chemical structure.

To uncover out the Lewis framework of I3, permit us inspect all the steps in the adhering to process.

Step 1

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

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

The first one stands for electron loss while the last signifies the soaking up or gain of negatively charged electrons hence increasing the negative charge the the molecule.

Step 2

After we have measured the total variety of valence electrons, we have actually to uncover out i m sorry one is the main atom.

In stimulate to execute so, we require to examine the atom having actually the highest valence i.e. The least electronegative one. This central atom is going to have actually a larger variety of bonding sites with respect come the other elements.

Step 3

The 3rd step is based on sketching the skeleton diagram of the offered molecule. This is done to visualize the single bonds in the positions the they room present.

Step 4

Most of you are currently familiar with the ax ‘octet rule’. That is basically a thumb ascendancy that claims that every atom the a molecule demands to have eight valence electron (electron count in the outermost shell).

So, ours duty here is to execute the octet completion. Because that your very own ease, shot to start with the electropositive persons first.

Step 5

After we have completed octets of atoms around other atoms, we should verify whether an ext bonds are needed to it is in formed.

Double binding or if necessary triple bonds are hence formed.

Step 6

We are currently done with all type of bond formation, The last action is focused on the formal fee concept.

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

Calculation of formal charge is excellent by simply following this straightforward formula.


For I3 (Triiodide ion)

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

We likewise have secondary 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 every the atoms room iodine, among these plays the role of the central atom.


3. As you can see in the above diagram, the skeletal framework of I3 with the an adverse charge has been drawn.

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

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

Hence, the iodine atom in ~ the center in in between the other two atom is walk to have 3 lone pairs(6) electrons through itself.

Forming the solitary bonds with the other two iodine, we find out that there room 3 lone pairs and 2 bond pairs because that the main iodine.

5. Check the formal charge, we placed the an unfavorable charge external as every the diagram above.Thus, lewis structure is done.

Hybridization of I3

The hybridization of I3 (Triiodide ion) is sp3d.

The means we draw the structure of molecular compounds on document is simply a two-dimensional form.

The understanding of chemistry reactions and also physical properties deserve to be better understood v the image in a 3-dimensional platform.

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

A straightforward formula to inspect out the hybridization number is:


Where, C= fee of cations; A=charge that anions, V= the total variety of valence electrons, M= Monovalent atoms and also H means the can be fried hybridization value.

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

therefore, H= 5

As every knowledge, since sp hybridization value is 2, likewise we can uncover out the for H=5, the form is sp3d.

Molecular Geometry the I3

If we take one more look in ~ the Lewis structure of the ion I3-, us can quickly see the the main iodine has three lone pairs.

The lone pairs space positioned equatorially due to repulsion.

Hence, the various other two iodine atoms are inserted axially and the bond angle made is 1800.

If we have focused on the formal fee theory, we know that it is the main atom that has actually the an unfavorable charge, therefore the donor.

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



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

Although the molecule geometry is straight as discussed earlier, the electronic geometry is trigonal bipyramidal.The structure of triiodide ion is such that the middle atom tote the ‘-’ charge.

Now, as we comment on polarity, permit us define it.

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

Dipole moment, thus, is a measure of polarity and is a an outcome of electronegativity distinction inside a molecule.

It usually arisen due to the separation of confident and an unfavorable charges and also depends top top the distance in between them.

Here, if we examine I3- has actually a an adverse charge but likewise it is symmetry in molecule geometry through no result dipole moment. Instead, the total charge of the molecule is an adverse as deciphered earlier.

So, even if it is to call this triiodide ion a polar or nonpolar molecule is a object of debate however if we look in ~ the solubility factor, we deserve to infer that it is polar( I3- is soluble in water).

I3 MO (Molecular Orbital) Diagram

Triiodide ion is a shining instance of 3-center-4-electron chemical bonding.

Now, what does it signify?


Before that, a brief an overview of MO or molecule Orbital concept is placed before you.

Now, as most of us space aware, a molecular orbital is a role to know the location and wave-like nature, thus, a delocalized method to bonding.

A MO can have a maximum of 2 electrons. MO results from overlapping between AO(atomic orbitals) of the exact same energy.

In the case of I3-, the no. Of valence electron is 22. One atom that iodine has actually the valence orbitals in the listed below fashion:5s, 5px, 5py, 5pz

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

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


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

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

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This sure will aid you recognize the physical and also chemical properties of compounds having actually I3- in a far better fashion.