CO Lewis Structure

CO Lewis Structure

CO (carbon monoxide) has one carbon atom and one oxygen atom. In the lewis structure of CO, there is a triple bond between the carbon and oxygen atom, and on both carbon and oxygen atoms, there is one lone pair.

Also, there is a negative (-1) charge on the carbon atom, and a positive (+1) charge on the oxygen atom.

Steps

Here’s how you can draw the CO lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: convert lone pair and mark charges again (if central atom doesn’t form octet)

Let’s break down each step in detail.

#1 Draw Sketch

  • First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, and oxygen lies in group 16.

Hence, carbon has four valence electrons and oxygen has six valence electrons.

Since CO has one carbon atom and one oxygen atom, so…

Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of one oxygen atom = 6 × 1 = 6

And the total valence electrons = 4 + 6 = 10

  • Second, find the total electron pairs

We have a total of 10 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 = 10 ÷ 2 = 5

  • 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.

  • And finally, draw the rough sketch
CO Lewis Structure (Step 1)

#2 Mark Lone Pairs

Here, we have a total of 5 electron pairs. And one C — O bond is already marked. So we have to only mark the remaining four 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 atom is oxygen.

So for oxygen, there are three lone pairs, and for carbon, there is one lone pair.

Mark the lone pairs on the sketch as follows:

CO Lewis Structure (Step 2)

#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 – 2 – ½ (2) = +1

For 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:

CO Lewis Structure (Step 3)

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:

CO Lewis Structure (Step 4)

In the above structure, you can see that the central atom (carbon) doesn’t form an octet. Hence, the octet rule is not satisfied.

#5 Convert Lone Pair and Mark Charges Again

Therefore, again convert a lone pair of the oxygen atom to make a new C — O bond with the carbon atom. Also, we have to again check whether there are charges on atoms or not.

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 – 2 – ½ (6) = -1

For oxygen atom, formal charge = 6 – 2 – ½ (6) = +1

Here, both carbon and oxygen atoms have charges, so mark them on the sketch as follows:

CO Lewis Structure (Step 5)

In the above structure, you can see that the central atom (carbon) 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 carbon 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 CO.

Next: CH4 Lewis Structure

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