I3- Lewis Structure in 5 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

I3- (triiodide) lewis structure has three Iodine atoms (I). There are 2 single bonds between each Iodine atom (I). There are 3 lone pairs on all the three Iodine atom. There is a -1 formal charge on the central Iodine atom (I).

If you haven’t understood anything from the above image of I3- (triiodide) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of I3- ion.

So let’s move to the steps of drawing the lewis structure of I3- ion.

Steps of drawing I3- lewis structure

Step 1: Find the total valence electrons in I3- ion

In order to find the total valence electrons in I3- (triiodide) ion, first of all you should know the valence electrons present in a single iodine atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of iodine using a periodic table.

Total valence electrons in I3- ion

→ Valence electrons given by iodine atom:

Iodine is a group 17 element on the periodic table. ^[1] Hence the valence electrons present in iodine is 7.

You can see the 7 valence electrons present in the iodine atom as shown in the above image.

Hence, 

Total valence electrons in I3- ion = valence electrons given by 3 iodine atoms + 1 more electron is added due to 1 negative charge = 7(3) + 1 = 22.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

Now here the given molecule is I3. All the three atoms are same, so you can select any of the atoms as a center atom.

Step 3: Connect each atoms by putting an electron pair between them

Now in the I3 molecule, you have to put the electron pairs between all three iodine atoms (I).

This indicates that all three iodine (I) atoms are chemically bonded with each other in an I3 molecule.

Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of I3 molecule, you can see that the outer atoms are iodine atoms only.

These outer iodine atoms are forming an octet and hence they are stable. 

Also, in step 1 we have calculated the total number of valence electrons present in the I3- ion.

The I3- ion has a total 22 valence electrons and out of these, only 16 valence electrons are used in the above sketch.

So the number of electrons which are left = 22 – 16 = 6.

You have to put these 6 electrons on the central iodine atom in the above sketch of I3 molecule.

Now let’s proceed to the next step.

Step 5: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of I3.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on all the iodine (I) atoms present in the I3 molecule.

For calculating the formal charge, you have to use the following formula;

Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons

You can see the number of bonding electrons and nonbonding electrons for each atom of I3 molecule in the image given below.

For central Iodine (I) atom:
Valence electrons = 7 (because iodine is in group 17)
Bonding electrons = 4
Nonbonding electrons = 6

For outer Iodine (I) atoms:
Valence electrons = 7 (because iodine is in group 17)
Bonding electrons = 2
Nonbonding electrons = 6

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
I (central)	=	7	–	4/2	–	6	=	-1
I (outer)	=	7	–	2/2	–	6	=	0

From the above calculations of formal charge, you can see that the central iodine (I) atom has -1 charge and the outer iodine atoms has 0 charges.

So let’s keep these charges on the respective atoms in the I3 molecule.

This overall -1 charge on the I3 molecule is represented in the image given below.

In the above lewis dot structure of I3- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of I3- ion.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

PF3 lewis structure	PCl5 lewis structure
H2O2 lewis structure	F2 lewis structure
CH2Cl2 lewis structure	ClO2- lewis structure