Lewis structure of CH3NCO

The information on this page is ✔ fact-checked.

The Lewis structure of CH₃NCO illustrates the arrangement of atoms in methyl isocyanate – a compound composed of one carbon, three hydrogen, one nitrogen, and one oxygen. The structure displays four single bonds and two double bonds, with carbon, nitrogen, and oxygen all aligned in a straight line.

On the left, the first carbon is single-bonded to three hydrogen atoms and one nitrogen atom. This nitrogen is then double-bonded to the second carbon, which, in turn, forms another double bond with an oxygen atom. Carbon and hydrogen atoms lack any lone pairs, while one lone pair is present on the nitrogen atom and two lone pairs exist on the oxygen atom.

To accurately draw the Lewis structure of CH₃NCO, follow these steps: Start by creating a rough sketch of the structure, then depict chemical bonds between each atom and mark lone pairs. Ensure the octet rule is satisfied for the central and other atoms. As a final step, verify the structure’s stability by calculating formal charges for each atom. The goal is to achieve a stable Lewis structure with minimal formal charges.

Steps

Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… carbon is a group 14 element, hydrogen is a group 1 element, nitrogen is a group 15 element, and oxygen is a group 16 element. Hence, carbon has four valence electrons, hydrogen has one valence electron, nitrogen has five valence electrons, and oxygen has six valence electrons.

Now CH₃NCO has two carbon atoms, three hydrogen atoms, one nitrogen atom, and one oxygen atom.

So the total number of valence electrons = (valence electrons of carbon atom × 2) + (valence electrons of hydrogen atom 3) + valence electrons of nitrogen atom + valence electrons of oxygen atom

Therefore, the total number of valence electrons = 8 + 3 + 5 + 6 = 22

• Now decide the central atom

We can not assume hydrogen as the central atom, because the central atom is bonded with at least two other atoms. And hydrogen has only one electron in its last shell, so it can not make more than one bond.

Therefore, choose the central atom from carbon, nitrogen, and oxygen.

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for carbon, nitrogen, and oxygen as follows:

Electronegativity value of carbon = 2.55
Electronegativity value of nitrogen = 3.04
Electronegativity value of oxygen = 3.44

Obviously, carbon is less electronegative than nitrogen and oxygen. Hence, assume that right carbon is the central atom (as there are two carbons).

So now, put two carbons and nitrogen in the center and oxygen and three hydrogens on either side. And draw the rough skeleton structure for the Lewis structure of CH₃NCO something like this:

Also read: How to draw Lewis structure of CO₂ (5 steps)

Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since two carbons and nitrogen are surrounded by oxygen and three hydrogens, use twelve electrons to show six chemical bonds as follows:

Mark lone pairs

As calculated earlier, we have a total of 22 valence electrons. And in the above structure, we have already used twelve valence electrons. Hence, ten valence electrons are remaining.

Two valence electrons represent one lone pair. So ten valence electrons = five lone pairs.

Note that all (carbon, nitrogen, and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell. And hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are hydrogens, oxygen, nitrogen, and left carbon. But hydrogen can not keep more than 2 electrons in its last shell. Hence, don’t mark the lone pairs on hydrogen.

So oxygen will get three lone pairs, and nitrogen will get two lone pairs. And the left carbon and central atom (right carbon) will not get any lone pair, because all five lone pairs are used.

Now draw the Lewis structure of CH₃NCO something like this:

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (right carbon) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of H₂O (4 steps)

Complete octet on atoms by calculating formal charge

Remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now right carbon already has four valence electrons. Hence, right carbon needs four more valence electrons to complete its octet.

Which means that we have to convert two lone pairs. But the question is, which lone pair should we convert to get the best Lewis structure?

There are three possible ways we can convert lone pair: 

1) Convert one lone pair from the nitrogen atom, and one lone pair from the oxygen atom.
2) Convert two lone pairs from the nitrogen atom.
3) Convert two lone pairs from the oxygen atom.

The best way to predict which lone pair should be converted to get the best Lewis structure is by calculating formal charges.

The following formula is used to calculate the formal charges on atoms:

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

Collect the data from the above structure and then, write it down below as follows:

• For left carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• For right carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 4

Formal charge = 4 – 0 – ½ (4) = +2

• For each hydrogen atom

Valence electrons = 1
Nonbonding electrons = 0
Bonding electrons = 2

Formal charge = 1 – 0 – ½ (2) = 0

• For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 5 – 4 – ½ (4) = -1

• For oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of CH₃NCO looks something like this:

In order to get the best Lewis structure, we have to make the formal charges on atoms closer to zero. And we can do so by choosing the 1).

So convert one lone pair from the nitrogen atom and oxygen atom to make a new bond with the carbon atom. And then, the Lewis structure of CH₃NCO looks something like this:

In the above structure, you can see that the octet is completed on the central atom (right carbon), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of NO₂ (5 steps)

Calculate formal charge again and check stability

The following formula is used to calculate the formal charges on atoms:

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

Collect the data from the above structure and then, write it down below as follows:

• For each carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• For each hydrogen atom

Valence electrons = 1
Nonbonding electrons = 0
Bonding electrons = 2

Formal charge = 1 – 0 – ½ (2) = 0

• For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 2
Bonding electrons = 6

Formal charge = 5 – 2 – ½ (6) = 0

• For oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of CH₃NCO looks something like this:

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of CH₃NCO.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

📝 Your feedback matters. Visit our contact page.

Related

• Lewis structure of CO₂
• Lewis structure of H₂O
• Lewis structure of NO₂
• Lewis structure of NH₃
• Lewis structure of HCN

External links

• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – Homework.Study.com
• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – Chegg
• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – Brainly
• Methyl Isocyanate | CH3NCO | CID 12228 – National Institutes of Health (.gov)
• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – Bartleby
• How do I compare the bond angle at N of CH3NCO & SiH3NCO? – Quora
• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – OneClass
• Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons – Vaia
• Methyl isocyanate | C2H3NO – ChemSpider