Lewis structure of CH2CHCN

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The Lewis structure of CH₂CHCN contains four single bonds, one double bond, and one triple bond, with three carbons in the center, and nitrogen and three hydrogens on either side. The left carbon is attached with two hydrogens, center carbon is attached with one hydrogen, and right carbon is attached with one nitrogen. There is one lone pair on the nitrogen atom, and carbon atom and hydrogen atom do not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of CH₂CHCN.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on atoms
#5 Calculate formal charge and check stability

Let’s one by one discuss each step in detail.

#1 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, and nitrogen is a group 15 element. Hence, carbon has four valence electrons, hydrogen has one valence electron, and nitrogen has five valence electrons.

Now CH₂CHCN has three carbon atoms, three hydrogen atoms, and one nitrogen atom.

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

Therefore, the total number of valence electrons = 12 + 3 + 5 = 20

• 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 and nitrogen.

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 and nitrogen as follows:

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

Obviously, carbon is less electronegative than nitrogen. Hence, assume that center carbon is the central atom (as there are three carbons).

So now, put three carbons in the center and nitrogen and three hydrogens on either side. And draw the rough skeleton structure for the Lewis structure of CH₂CHCN something like this:

Also read: How to draw Lewis structure of TeBr₄ (4 steps)

#2 Show chemical bond

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

#3 Mark lone pairs

As calculated earlier, we have a total of 20 valence electrons. And in the above structure, we have already used twelve valence electrons. Hence, eight valence electrons are remaining.

Two valence electrons represent one lone pair. So eight valence electrons = four lone pairs.

Note 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.

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

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

Now draw the Lewis structure of CH₂CHCN something like this:

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

So in the next step, we have to complete the octet on center carbon and right carbon.

Also read: How to draw Lewis structure of GeH₄ (3 steps)

#4 Complete octet on atoms

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

Now center carbon already has six valence electrons. Hence, center carbon needs two more valence electrons to complete its octet.

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

So convert one lone pair from the left carbon atom to make a new bond with the center carbon atom, and two lone pairs from the nitrogen atom to make a new bond with the right carbon atom.

And then, the Lewis structure of CH₂CHCN looks something like this:

In the above structure, you can see that the octet is completed on the central atom (center 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 HOF (4 steps)

#5 Calculate formal charge 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 hydrogen atom

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

Formal charge = 1 – 0 – ½ (2) = 0

• For each carbon atom

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

Formal charge = 4 – 0 – ½ (8) = 0

• For nitrogen atom

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

Formal charge = 5 – 2 – ½ (6) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of CH₂CHCN 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 CH₂CHCN.

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

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Related

• Lewis structure of TeBr₄
• Lewis structure of GeH₄
• Lewis structure of HOF
• Lewis structure of XeCl₄
• CH₃⁺ Lewis structure

External links

• CH2CHCN geometry – CHEMISTRY COMMUNITY – Laurence Lavelle
• Draw the proper Lewis structure of CH2CHCN – Quizlet
• Provide a Lewis structure and a complete labeled sketch of CH2CHCN – Numerade
• Draw the Lewis structure of CH2CHCN – Chegg
• What is the IUPAC name of CH2CHCN? – Quora
• Acrylonitrile | H2CCHCN | CID 7855 – National Institutes of Health (.gov)