Lewis structure of C2H2

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The Lewis structure of C₂H₂ contains one triple bond and two single bonds, with two carbons in the center, and each carbon is attached with one hydrogen. Both hydrogen atom and carbon atom do not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of C₂H₂:

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#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 and hydrogen is a group 1 element. Hence, carbon has four valence electrons and hydrogen has one valence electron.

Now C₂H₂ has two carbon atoms and two hydrogen atoms.

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

Therefore, the total number of valence electrons = 8 + 2 = 10

• 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 carbon as the central atom.

But there are two carbon atoms in C₂H₂. Hence, we can assume any one as the central atom. Let’s assume that left carbon is the central atom.

So now, put two carbons in the center and two hydrogens on either side. And draw the rough skeleton structure for the Lewis structure of C₂H₂ something like this:

Also read: How to draw Lewis structure of SF₄ (4 steps)

#2 Show chemical bond

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

#3 Mark lone pairs

As calculated earlier, we have a total of 10 valence electrons. And in the above structure, we have already used six valence electrons. Hence, four valence electrons are remaining.

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

Note that carbon is a period 2 element, so it can not keep more than 8 electrons in its 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 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 right carbon will get two lone pairs. And the central atom (left carbon) will not get any lone pair, because all two lone pairs are used.

Now draw the Lewis structure of C₂H₂ something like this:

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (left 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 CCl₄ (4 steps)

#4 Complete octet on central atom

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

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

So convert two lone pairs from the right carbon atom to make a new bond with the left carbon atom. And then, the Lewis structure of C₂H₂ looks something like this:

In the above structure, you can see that the octet is completed on the central atom (left 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 OF₂ (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 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

Mention the formal charges of atoms on the structure. So the Lewis structure of C₂H₂ looks something like this:

In the above structure, you can see that the formal charges of both (carbon and hydrogen) are zero. Therefore, this is the stable Lewis structure of C₂H₂.

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

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Related

• Lewis structure of SF₄
• Lewis structure of CCl₄
• Lewis structure of OF₂
• Lewis structure of CS₂
• Lewis structure of NO

External video

• How to Draw the Lewis Dot Structure for C2H2: Acetylene (Ethyne) – Wayne Breslyn

External links

• Lewis Structure for C2H2 (Ethyne) – The University of Maryland
• C2H2 Lewis Structure in 6 Steps (With Images) – Pediabay
• C2H2 Lewis structure, Molecular Geometry, Hybridization & Bond angle – Geometry of Molecules
• C2H2 lewis structure, molecular geometry, bond angle, hybridization – Topblogtenz
• C2H2 (Acetylene | Ethyne) Lewis Structure – Chemistry School
• C2H2 Lewis Structure, Molecular Geometry, Hybridization, Polarity, and MO Diagram – Techiescientist
• C2H2 Lewis Structure, Geometry – Kemicalinfo
• Draw the Lewis structure for acetylene (C2H2) – Chegg
• Draw the Lewis structure for C2H2 – Homework.Study.com
• Write the Lewis structure for C2H2 – Studocu
• Which is the correct Lewis structure for acetylene (C2H2)? – Brainly
• Lewis Dot of Ethyne (Acetylene) C2H2 – Kent’s Chemistry
• The best Lewis structure for ethyne (C2H2; commonly called “acetylene”) – Numerade
• Draw the Lewis structure of ethyne – Course Hero
• File:C2H2 Lewis.png – Wikimedia Commons