C22- Lewis structure

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C₂^2- (acetylide) has two carbon atoms.

In the C₂^2- Lewis structure, there is a triple bond between the two carbon atoms, and on each carbon atom, there is one lone pair.

Also, there is a negative (-1) charge on each carbon atom.

Steps

Here’s how you can draw the C₂^2- Lewis structure step by step:

#1 Draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Mark charges on the atoms
#4 Minimize charges by converting lone pairs
#5 If central atom doesn’t form octet, convert lone pair and mark charges again

Let’s break down each step in detail.

#1 Draw a rough sketch

• First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14. Hence, carbon has four valence electrons.

Since C₂^2- has two carbon atoms, so…

Valence electrons of two carbon atoms = 4 × 2 = 8

Now the C₂^2- has a negative (-2) charge, so we have to add two more electrons.

So the total valence electrons = 8 + 2 = 10

Learn how to find: Carbon valence electrons

• Second, find the total electron pairs

We have a total of 10 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 = 10 ÷ 2 = 5

• Third, determine the central atom

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

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

• And finally, draw the rough sketch

#2 Mark lone pairs on the atoms

Here, we have a total of 5 electron pairs. And one C — C bond is already marked. So we have to only mark the remaining four electron pairs as lone pairs on the sketch.

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

Always start to mark the lone pairs from outside atoms. Here, the outside atom is right carbon.

So for right carbon, there are three lone pairs, and for left carbon, there is one lone pair.

Mark the lone pairs on the sketch as follows:

#3 Mark charges on the atoms

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 – 2 – ½ (2) = +1

For right carbon atom, formal charge = 4 – 6 – ½ (2) = -3

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

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

#4 Minimize charges by converting lone pairs

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

In the above structure, you can see that the central atom (left carbon) doesn’t form an octet. Hence, the octet rule is not satisfied.

#5 Convert lone pair and mark charges again

Therefore, again convert a lone pair of the right carbon atom to make a new C — O bond with the left carbon atom. Also, we have to again check whether there are charges on atoms or not.

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 – 2 – ½ (6) = -1

For right carbon atom, formal charge = 4 – 2 – ½ (6) = -1

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

In the above structure, you can see that the central atom (left carbon) forms an octet. And the outside atom (right carbon) also forms an octet. Hence, the octet rule is satisfied.

Now there is a negative (-1) charge on each carbon atom.

This is okay, because the structure with a negative charge on the most electronegative atom is the best Lewis structure. And in this case, the most electronegative element is carbon.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the most stable Lewis structure of C₂^2-.

And since the C₂^2- has a negative (-2) charge, mention that charge on the Lewis structure by drawing brackets as follows:

Next: H₂SO₃ Lewis structure

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External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/C22–lewis-structure.html
• https://www.chemistryscl.com/general/carbide-C2-2–ion-lewis-structure/index.php