Lewis Structure of C2H2 (With 6 Simple Steps to Draw!) (2024)

Lewis structure of C2H2 (or Acetylene or Ethyne) contains one triple bond between the two Carbon (C) atoms and two single bonds between Carbon (C) & Hydrogen (H) atoms.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of C2H2).

6 Steps to Draw the Lewis Structure of C2H2

Step #1: Calculate the total number of valence electrons

Here, the given molecule is C2H2 (or ethyne or acetylene). In order to draw the lewis structure of C2H2, first of all you have to find the total number of valence electrons present in the C2H2 molecule.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in C2H2

• For Carbon:

Carbon is a group 14 element on the periodic table. ^[1]

Hence, the valence electrons present in carbon is 4 (see below image).

• For Hydrogen:

Hydrogen is a group 1 element on the periodic table. ^[2]

Hence, the valence electron present in hydrogen is 1 (see below image).

Hence in a C2H2 molecule,

Valence electrons given by each Carbon (C) atom = 4
Valence electron given by each Hydrogen (H) atom = 1
So, total number of Valence electrons in C2H2 molecule = 4(2) + 1(2) = 10

Step #2: Select the center atom (H is always outside)

While selecting the center atom, always put the least electronegative atom at the center.

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). [3]

Here in the C2H2 molecule, if we compare the carbon atom (C) and hydrogen atom (H), then hydrogen is less electronegative than carbon. But as per the rule, we have to keep hydrogen outside.

So, both the carbon atoms should be placed in the center and the remaining 2 hydrogen atoms will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of C2H2 molecule, put the two electrons (i.e electron pair) between the carbon-carbon atoms and carbon-hydrogen atoms to represent a chemical bond between them.

These pairs of electrons present between the Carbon atoms as well as between the Carbon and Hydrogen atoms form a chemical bond, which bonds these atoms with each other in a C2H2 molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of C2H2, the outer atoms are hydrogen atoms.

So now, you have to check whether these hydrogen atoms are forming a duplet or not! (because hydrogen requires only 2 electrons to have a complete outer shell).

You can see in the above image that both the hydrogen atoms form a duplet.

Also, only 6 valence electrons of C2H2 molecule are used in the above structure.

But there are total 10 valence electrons in C2H2 molecule (as calculated in step #1).

So the number of electrons left to be kept on the central carbon atoms = 10 – 6 = 4.

So let’s keep these four electrons (i.e 2 electron pairs) on the central carbon atoms.

Now, let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then convert the lone pair into double bond or triple bond

In this step, we have to check whether the central atoms (i.e two carbon atoms) have an octet or not.

In simple words, we have to check whether the central Carbon (C) atoms has 8 electrons or not.

As you can see from the above image, the central atoms has only 6 electrons. So they do not fulfill the octet rule.

Now, in order to fulfill the octet of carbon atoms, we have to convert the lone pair into a double bond.

Still, the octet of other carbon atom is not fulfilled.

So again converting the lone pair into the bond, we will get the following structure.

Now you can see from the above image that both the central carbon atoms are having 8 electrons. So they fulfill the octet rule and both the carbon atoms are stable.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on carbon atoms (C) as well as hydrogen atoms (H).

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

• For Carbon:
  Valence electrons = 4 (as it is in group 14)
  Nonbonding electrons = 0
  Bonding electrons = 8
• For Hydrogen:
  Valence electron = 1 (as it is in group 1)
  Nonbonding electrons = 0
  Bonding electrons = 2

So you can see above that the formal charges on carbon as well as hydrogen are “zero”.

Hence, there will not be any change in the above structure and the above lewis structure of C2H2 is the final stable structure only.

Each electron pair (:) in the lewis dot structure of C2H2 represents the single bond ( | ). So the above lewis dot structure of C2H2 can also be represented as shown below.

Related lewis structures for your practice:
Lewis structure of CH2O
Lewis structure of SO3
Lewis structure of C2H4
Lewis structure of SF4
Lewis structure of H2S

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