CH3NO2 Lewis structure

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CH₃NO₂ (nitromethane) has one carbon atom, three hydrogen atoms, one nitrogen atom, and two oxygen atoms.

In the CH₃NO₂ Lewis structure, there is a single bond between the carbon and nitrogen atom. The carbon atom is attached with three hydrogen atoms, and the nitrogen atom is attached with two oxygen atoms. The oxygen atom with a single bond has three lone pairs, and the oxygen atom with a double bond has two lone pairs.

Also, there is a negative (-1) charge on the oxygen atom with a single bond, and a positive (+1) charge on the nitrogen atom.

Steps

Use these steps to correctly draw the CH₃NO₂ Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required
#4 Convert lone pairs of the atoms, and minimize formal charges
#5 Repeat step 4 if needed, until all charges are minimized, to get a stable Lewis structure

Let’s discuss each step in more detail.

#1 First draw a rough sketch

• First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, hydrogen lies in group 1, nitrogen lies in group 15, and oxygen lies in group 16.

Hence, carbon has four valence electrons, hydrogen has one valence electron, nitrogen has five valence electrons, and oxygen has six electrons.

Since CH₃NO₂ has one carbon atom, three hydrogen atoms, one nitrogen atom, and two oxygen atoms, so…

Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of three hydrogen atoms = 1 × 3 = 3
Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of two oxygen atoms = 6 × 2 = 12

And the total valence electrons = 4 + 3 + 5 + 12 = 24

Learn how to find: Carbon valence electrons, Hydrogen valence electrons, Nitrogen valence electrons, and Oxygen valence electrons

• Second, find the total electron pairs

We have a total of 24 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 = 24 ÷ 2 = 12

• Third, determine the central atom

Here hydrogen can not be 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.

Now we have to choose the central atom from carbon, nitrogen, and oxygen. Place the least electronegative atom at the center.

Since carbon is less electronegative than nitrogen and oxygen, assume that the central atom is carbon.

Therefore, place carbon in the center and hydrogen, nitrogen, and oxygen on either side.

• And finally, draw the rough sketch

#2 Mark lone pairs on the atoms

Here, we have a total of 12 electron pairs. And six bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.

Also remember that all three (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.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens, nitrogen, and oxygens. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for each oxygen, there are three lone pairs, and for nitrogen and carbon, there is zero lone pair because all six electron pairs are over.

Mark the lone pairs on the sketch as follows:

#3 Calculate and mark formal charges on the atoms, if required

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 (8) = 0

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

For nitrogen atom, formal charge = 5 – 0 – ½ (6) = +2

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

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

The above structure is not a stable Lewis structure because both nitrogen and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

#4 Convert lone pairs of the atoms, and minimize formal charges

Convert a lone pair of the oxygen atom to make a new N — O bond with the nitrogen atom as follows:

In the above structure, you can see that the central atom (nitrogen) forms an octet. The outside atoms (carbon and oxygens) also form an octet, and all hydrogens form a duet. Hence, the octet rule and duet rule are satisfied.

Now there are still charges on the atoms. But we can not convert a lone pair to a bond because nitrogen 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 CH₃NO₂.

Next: AsH₃ Lewis structure

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External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/CH3NO2-lewis-structure.html
• https://techiescientist.com/ch3no2-lewis-structure/
• https://lambdageeks.com/ch3no2-lewis-structure/