CH3CN Lewis structure

CH₃CN (acetonitrile) has two carbon atoms, three hydrogen atoms, and one nitrogen atom.

In the CH₃CN Lewis structure, there is a single bond between the two carbon atoms. The left carbon is attached with three hydrogen atoms, and the right carbon makes a triple bond with one nitrogen atom. And on the nitrogen atom, there is one lone pair.

Alternative method: Lewis structure of CH₃CN

Rough sketch

• First, determine the total number of valence electrons

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

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

Since CH₃CN has two carbon atoms, three hydrogen atoms, and one nitrogen atom, so…

Valence electrons of two carbon atoms = 4 × 2 = 8
Valence electrons of three hydrogen atoms = 1 × 3 = 3
Valence electrons of one nitrogen atom = 5 × 1 = 5

And the total valence electrons = 8 + 3 + 5 = 16

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

• 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

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 and nitrogen. Place the least electronegative atom at the center.

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

Here, there are two carbon atoms, so we can assume any one as the central atom.

Let’s assume that the central atom is right carbon.

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

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 8 electron pairs. And five bonds are already marked. So we have to only mark the remaining three electron pairs as lone pairs on the sketch.

Also remember that both (carbon and nitrogen) 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 and nitrogen. But no need to mark on hydrogen, because each hydrogen has already two electrons.

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

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

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

For left carbon atom, formal charge = 4 – 0 – ½ (8) = 0

For right carbon atom, formal charge = 4 – 0 – ½ (4) = +2

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

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

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

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

Convert a lone pair of the nitrogen atom to make a new C — N bond with the right carbon atom as follows:

Since there are charges on carbon and nitrogen atoms, again convert a lone pair of the nitrogen atom to make a new C — N bond with the right carbon atom as follows:

Final structure

The final structure of CH₃CN has a central carbon atom bonded to three hydrogen atoms and a second carbon atom through single covalent bonds. This second carbon atom is further linked to a nitrogen atom via a triple bond, completing the linear nitrile group. In this arrangement, both carbon atoms and the nitrogen atom satisfy the octet rule, while the hydrogen atoms achieve their stable duets. This configuration results in formal charges of zero for all atoms, ensuring the molecule reaches its most energetically favorable state. Consequently, this specific bonding pattern represents the stable and definitive Lewis representation of acetonitrile.

Next: IF₄^– Lewis structure

External video

• How to Draw the Lewis Dot Structure for CH3CN: Acetonitrile – YouTube • Wayne Breslyn

External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/CH3CN-lewis-structure.html
• https://topblogtenz.com/acetonitrile-ch3cn-lewis-dot-structure-molecular-geometry-polarity/
• https://techiescientist.com/ch3cn-lewis-structure/