NI3 Lewis structure

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NI3 Lewis Structure
NI3 Lewis structure

NI3 (nitrogen triiodide) has one nitrogen atom and three iodine atoms.

In the NI3 Lewis structure, there are three single bonds around the nitrogen atom, with three iodine atoms attached to it. Each iodine atom has three lone pairs, and the nitrogen atom has one lone pair.


Use these steps to correctly draw the NI3 Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required

Let’s discuss each step in more detail.

#1 First draw a rough sketch

  • First, determine the total number of valence electrons
Periodic table

In the periodic table, nitrogen lies in group 15, and iodine lies in group 17.

Hence, nitrogen has five valence electrons and iodine has seven valence electrons.

Since NI3 has one nitrogen atom and three iodine atoms, so…

Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of three iodine atoms = 7 × 3 = 21

And the total valence electrons = 5 + 21 = 26

  • Second, find the total electron pairs

We have a total of 26 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 = 26 ÷ 2 = 13

  • Third, determine the central atom

We have to place the least electronegative atom at the center.

Since iodine is less electronegative than nitrogen, the central atom should be iodine, right?

But if we place iodine in the center and nitrogen outside, and calculate the formal charge, then we do not get the formal charges on atoms closer to zero.

And the structure with the formal charges on atoms closer to zero is the best Lewis structure.

Hence, here we have to assume that the central atom is nitrogen.

Therefore, place nitrogen in the center and iodines on either side.

  • And finally, draw the rough sketch
NI3 Lewis Structure (Step 1)
Rough sketch of NI3 Lewis structure

#2 Mark lone pairs on the atoms

Here, we have a total of 13 electron pairs. And three N — I bonds are already marked. So we have to only mark the remaining ten electron pairs as lone pairs on the sketch.

Also remember that nitrogen is a period 2 element, so it can not keep more than 8 electrons in its last shell. And 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 iodines.

So for each iodine, there are three lone pairs, and for nitrogen, there is one lone pair.

Mark the lone pairs on the sketch as follows:

NI3 Lewis Structure (Step 2)
Lone pairs marked, and got the stable Lewis structure of NI3

#3 Calculate and mark formal charges on the atoms, if required

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

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

For nitrogen atom, formal charge = 5 – 2 – ½ (6) = 0

For each iodine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, both nitrogen and iodine atoms do not have charges, so no need to mark the charges.

In the above structure, you can see that the central atom (nitrogen) forms an octet. And the outside atoms (iodines) also form an octet. Hence, the octet rule is satisfied.

Therefore, this structure is the stable Lewis structure of NI3.

Next: CH2F2 Lewis structure

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