N3– (azide) has three nitrogen atoms. In the lewis structure of N3–, there are two double bonds around the nitrogen atom, with two other nitrogen atoms attached to it, and on left and right nitrogen atoms, there are two lone pairs.
Also, there is a negative (-1) charge on the left and right nitrogen atoms, and a positive (+1) charge on the center nitrogen atom.
Here’s how you can draw the I3– lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Since N3– has three nitrogen atoms, so…
Valence electrons of three nitrogen atoms = 5 × 3 = 15
Now the N3– has a negative (-1) charge, so we have to add one more electron.
So the total valence electrons = 15 + 1 = 16
- Second, find the total electron pairs
We have a total of 16 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 = 16 ÷ 2 = 8
- Third, determine the central atom
Here, there are three atoms and all atoms are nitrogen, so we can assume any one as the central atom.
Let’s assume that the central atom is center nitrogen.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 8 electron pairs. And two N — N bonds are already marked. So we have to only mark the remaining six 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.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are left nitrogen and right nitrogen.
So for left nitrogen and right nitrogen, there are three lone pairs, and for canter nitrogen, there is zero lone pair because all six electron pairs are over.
Mark the lone pairs on the sketch as follows:
#3 Mark Charges
Use the following formula to calculate the formal charges on atoms:
Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons
For left nitrogen and right nitrogen atom, formal charge = 5 – 6 – ½ (2) = -2
For center nitrogen atom, formal charge = 5 – 0 – ½ (4) = +3
Here, all nitrogen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because all nitrogen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the left nitrogen atom to make a new N — N bond with the center nitrogen atom as follows:
#5 Minimize Charges Again
Since there are charges on nitrogen atoms, again convert a lone pair of the right nitrogen atom to make a new N — N bond with the center nitrogen atom as follows:
In the above structure, you can see that the central atom (center nitrogen) forms an octet. Hence, the octet rule is satisfied.
Now there are still charges on the atoms.
This is okay, because the structure with a negative charge on the most electronegative atom is the best lewis structure. And in this case, the most electronegative element is nitrogen.
Therefore, this structure is the most stable lewis structure of N3–.
And since the N3– has a negative (-1) charge, mention that charge on the lewis structure by drawing brackets as follows:
Next: BH3 Lewis Structure