I3- Lewis structure

I₃^– (triiodide) has three iodine atoms.

In the I₃^– Lewis structure, there are two single bonds around the iodine atom, with two other iodine atoms attached to it, and on each iodine atom, there are three lone pairs.

Also, there is a negative (-1) charge on the center iodine atom.

Alternative method: Lewis structure of I₃^–

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, iodine lies in group 17. Hence, iodine has seven valence electrons.

Since I₃^– has three iodine atoms, so…

Valence electrons of three iodine atoms = 7 × 3 = 21

Now the I₃^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 21 + 1 = 22

• Second, find the total electron pairs

We have a total of 22 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 22 ÷ 2 = 11

• Third, determine the central atom

Here, there are three atoms and all atoms are iodine, so we can assume any one as the central atom.

Let’s assume that the central atom is center iodine.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 11 electron pairs. And two I — I bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that iodine is a period 5 element, so it can keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are left iodine and right iodine.

So for each iodine, there are three lone pairs.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For left iodine and right iodine atom, formal charge = 7 – 6 – ½ (2) = 0

For center iodine atom, formal charge = 7 – 6 – ½ (4) = -1

Here, the center iodine atom has a charge, so mark it on the sketch as follows:

Final structure

The final structure of I₃^– contains a central iodine atom connected to two terminal iodine atoms through single covalent bonds. Within this layout, the central iodine atom utilizes an expanded octet to accommodate ten valence electrons, which include two bonding pairs and three lone pairs. Each terminal iodine atom fulfills its octet by maintaining three lone pairs of its own alongside the single shared bond. This arrangement is the most stable because it optimizes the distribution of formal charges; the terminal atoms carry a formal charge of zero, while the central atom carries the formal charge of -1. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the triiodide ion.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 1- is then written as a superscript outside the brackets at the top right, indicating that the structure possesses one additional electron beyond the valence count of the three neutral iodine atoms.

Next: CN^– Lewis structure

External video

• I3- Lewis Structure – How to Draw the Lewis Structure for I3- – YouTube • Wayne Breslyn

External links

• https://geometryofmolecules.com/i3-lewis-structure-shape-hybridization-polarity/
• https://www.chemistryscl.com/general/triiodide-I3–lewis-structure/index.php
• https://techiescientist.com/i3-lewis-structure/
• https://lambdageeks.com/i3-lewis-structure/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/I3-minus-lewis-structure.html