I’m super excited to teach you the lewis structure of I3- ion in just 5 simple steps.
Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of I3- ion.
So, if you are ready to go with these 5 simple steps, then let’s dive right into it!
Lewis structure of I3- ion (triiodide) contains two single bonds between each Iodine (I) atom. All the three Iodine atoms have three lone pairs on it, and the central iodine atom has -1 formal charge.
Let’s draw and understand this lewis dot structure step by step.
(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of I3- ion).
6 Steps to Draw the Lewis Structure of I3-
Step #1: Calculate the total number of valence electrons
Here, the given ion is I3–. In order to draw the lewis structure of I3– ion, first of all you have to find the total number of valence electrons present in the I3– ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).
So, let’s calculate this first.
Calculation of valence electrons in I3– ion
- For Iodine:
Iodine is a group 17 element on the periodic table. 
Hence, the valence electrons present in iodine is 7 (see below image).
Hence in a I3– ion,
Valence electrons given by each Iodine (I) atom = 7
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in I3– ion = 7(3) + 1 = 22
Step #2: Select the center atom
While selecting the atom, you have to put the least electronegative atom at the center.
But here in the I3- ion, all three atoms are same. So you can simply put any iodine atom at center and place other iodine atoms surrounding it.
Step #3: Put two electrons between the atoms to represent a chemical bond
Now in the above sketch of I3 molecule, put the two electrons (i.e electron pair) between all the three iodine atoms to represent a chemical bond between them.
These pair of electrons present between the Iodine (I) atoms form a chemical bond, which bonds all the iodine atoms with each other in a I3- ion.
Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom
Don’t worry, I’ll explain!
In the Lewis structure of I3– ion, the outer atoms are iodine atoms only.
So now, you have to complete the octet on these iodine atoms (because iodine requires 8 electrons to have a complete outer shell).
Also, only 16 valence electrons of I3- ion are used in the above structure.
But there are total 22 valence electrons in I3- ion (as calculated in step #1).
So the number of electrons left to be kept on the central atom = 22 – 16 = 6.
So let’s keep these six electrons (i.e three electron pairs) on the central iodine atom.
Now, let’s move to the next step.
Step #5: Check the formal charge
Now, you have come to the final step and here you have to check the formal charge on I3- ion.
For that, you need to remember the formula of formal charge;
Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2
- For central Iodine:
Valence electrons = 7 (as it is in group 17)
Nonbonding electrons = 6
Bonding electrons = 4
- For outer Iodine:
Valence electron = 7 (as it is in group 17)
Nonbonding electrons = 6
Bonding electrons = 2
|Formal charge||=||Valence electrons||–||Nonbonding electrons||–||(Bonding electrons)/2|
Let’s keep these charges on the atoms in the above lewis structure of I3– ion.
As you can see in the above sketch, there is one -ve charge on the central iodine atom, which indicates the -1 formal charge on the I3 molecule.
Hence, the above lewis structure of I3- ion is the stable lewis structure.
Each electron pair (:) in the lewis dot structure of I3- ion represents the single bond ( | ). So the above lewis dot structure of I3- ion can also be represented as shown below.
Related lewis structures for your practice:
Lewis structure of CN-
Lewis structure of PF3
Lewis structure of PCl5
Lewis structure of H2O2
Lewis structure of F2