C2H2 Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

C2H2 lewis structure has a triple bond between the two Carbon atoms (C) and a single bond between the Carbon atom (C) and Hydrogen atom (H).

If you haven’t understood anything from the above image of C2H2 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of C2H2.

So let’s move to the steps of drawing the lewis structure of C2H2.

Steps of drawing C2H2 lewis structure

Step 1: Find the total valence electrons in C2H2 molecule

In order to find the total valence electrons in C2H2 molecule, first of all you should know the valence electrons present in carbon atom as well as hydrogen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of carbon as well as hydrogen using a periodic table.

Total valence electrons in C2H2 molecule

→ Valence electrons given by carbon atom:

Carbon is group 14 element on the periodic table. ^[1] Hence the valence electrons present in carbon is 4.

You can see the 4 valence electrons present in the carbon atom as shown in the above image.

→ Valence electrons given by hydrogen atom:

Hydrogen is group 1 element on the periodic table. ^[2] Hence the valence electron present in hydrogen is 1.

You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.

Hence, 

Total valence electrons in C2H2 molecule = valence electrons given by 2 carbon atom + valence electrons given by 2 hydrogen atoms = 4(2) + 1(2) = 10.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)

Now here the given molecule is C2H2 (or acetylene or ethyne) and it contains carbon atom (C) and hydrogen atoms (H).

You can see the electronegativity values of carbon atom (C) and hydrogen atom (H) in the above periodic table.

If we compare the electronegativity values of carbon (C) and hydrogen (H) then the hydrogen atom is less electronegative. But as per the rule we have to keep hydrogen outside.

So here both the carbon atoms (C) are the center atom and the hydrogen atoms (H) are the outside atoms.

Step 3: Connect each atoms by putting an electron pair between them

Now in the C2H2 molecule, you have to put the electron pairs between the carbon-carbon atoms and between the carbon-hydrogen atoms.

This indicates that these atoms are chemically bonded with each other in a C2H2 molecule.

Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of C2H2 molecule, you can see that the outer atoms are hydrogen atoms.

These outer hydrogen atoms are forming a duplet and hence they are stable. 

Also, in step 1 we have calculated the total number of valence electrons present in the C2H2 molecule.

The C2H2 molecule has a total 10 valence electrons and out of these, only 6 valence electrons are used in the above sketch.

So the number of electrons which are left = 10 – 6 = 4.

You have to put these 4 electrons on both the central carbon atoms in the above sketch of C2H2 molecule.

Now let’s proceed to the next step.

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

In this step, you have to check whether the central carbon atoms (C) are stable or not.

In order to check the stability of the central carbon (C) atoms, we have to check whether they are forming an octet or not.

Unfortunately, both the carbon atoms are not forming an octet here. Both the carbon atoms have only 6 electrons and they are unstable.

Now to make the carbon atom stable, you have to convert the lone pair into double bond so that the carbon atom can have 8 electrons (i.e octet).

But after converting one electron pair, one carbon atom is forming an octet but the other carbon atom is still not forming an octet as it has only 6 electrons. 

So again we have to convert one more electron pair to form a triple bond.

After converting this electron pair into a triple bond, the central carbon atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that both the carbon atoms are forming an octet.

And hence these carbon atoms are stable.

Now let’s proceed to the final step to check whether the lewis structure of C2H2 is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of C2H2.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on carbon (C) atoms as well as hydrogen (H) atoms present in the C2H2 molecule.

For calculating the formal charge, you have to use the following formula;

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

You can see the number of bonding electrons and nonbonding electrons for each atom of C2H2 molecule in the image given below.

For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 8
Nonbonding electrons = 0

For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0

From the above calculations of formal charge, you can see that the carbon (C) atoms as well as hydrogen (H) atoms have a “zero” formal charge.

This indicates that the above lewis structure of C2H2 is stable and there is no further change in the above structure of C2H2.

In the above lewis dot structure of C2H2, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of C2H2.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

About author

Jay Rana

Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.

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