O3 (ozone) has three oxygen atoms. In the lewis structure of O3, there is one double bond and one single bond around the oxygen atom, with two other oxygen atoms attached to it. The oxygen atom with a double bond has two lone pairs, the oxygen atom with a single bond has three lone pairs, and the center oxygen atom has one lone pair.
Also, there is a positive (+1) charge on the center oxygen atom, and a negative (-1) charge on the oxygen atom with a single bond.
Here’s how you can draw the O3 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 O3 has three oxygen atoms, so…
Valence electrons of three oxygen atoms = 6 × 3 = 18
So the total valence electrons = 18
- Second, find the total electron pairs
We have a total of 18 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 = 18 ÷ 2 = 9
- Third, determine the central atom
Here, there are three atoms and all atoms are oxygen, so we can assume any one as the central atom.
Let’s assume that the central atom is center oxygen.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 9 electron pairs. And two O — O bonds are already marked. So we have to only mark the remaining seven electron pairs as lone pairs on the sketch.
Also remember that oxygen 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 oxygen and right oxygen.
So for left oxygen and right oxygen, there are three lone pairs, and for center oxygen, there is one lone pair.
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 oxygen and right oxygen atom, formal charge = 6 – 6 – ½ (2) = -1
For center oxygen atom, formal charge = 6 – 2 – ½ (4) = +2
Here, all oxygen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because all oxygen 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 oxygen atom to make a new O — O bond with the center oxygen atom as follows:
In the above structure, you can see that the central atom (center oxygen) forms an octet. Hence, the octet rule is satisfied.
Now there are still charges on the atoms. But we can not convert a lone pair to a bond because oxygen can not keep more than 8 electrons in its last shell.
The formal charges on atoms are closer to zero. Also, the above structure is more stable than the previous structures. Therefore, this structure is the most stable lewis structure of O3.
Next: C2H2 Lewis Structure