CO2 (carbon dioxide) has one carbon atom and two oxygen atoms.
In the lewis structure of CO2, there are two double bonds around the carbon atom, with two oxygen atoms attached to it, and on each oxygen atom, there are two lone pairs.
Here’s how you can draw the CO2 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
Hence, carbon has four valence electrons and oxygen has six valence electrons.
Since CO2 has one carbon atom and two oxygen atoms, so…
Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of two oxygen atoms = 6 × 2 = 12
And the total valence electrons = 4 + 12 = 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
We have to place the least electronegative atom at the center.
Since carbon is less electronegative than oxygen, assume that the central atom is carbon.
Therefore, place carbon in the center and oxygens on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 8 electron pairs. And two C — O bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.
Also remember that both (carbon and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygens.
So for each oxygen, there are three lone pairs, and for carbon, 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 carbon atom, formal charge = 4 – 0 – ½ (4) = +2
For each oxygen atom, formal charge = 6 – 6 – ½ (2) = -1
Here, both carbon and oxygen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both carbon and 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 oxygen atom to make a new C — O bond with the carbon atom as follows:
#5 Minimize Charges Again
Since there are charges on carbon and oxygen atoms, again convert a lone pair of the oxygen atom to make a new C — O bond with the carbon atom as follows:
In the above structure, you can see that the central atom (carbon) forms an octet. And the outside atoms (oxygens) also form an octet. Hence, the octet rule is satisfied.
Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of CO2.
Next: SO2 Lewis Structure