C2HCl (chloroethyne) has two carbon atoms, one hydrogen atom, and one chlorine atom. In the lewis structure of C2HCl, there is a triple bond between the two carbon atoms. The left carbon is attached with the hydrogen atom, and the right carbon is attached with the chlorine atom. And on the chlorine atom, there are three lone pairs.
Here’s how you can draw the C2HCl lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Hence, carbon has four valence electrons, hydrogen has one valence electron, and chlorine has seven valence electrons.
Since C2HCl has two carbon atoms, one hydrogen atom, and one chlorine atom, so…
Valence electrons of two carbon atoms = 4 × 2 = 8
Valence electrons of one hydrogen atom = 1 × 1 = 1
Valence electrons of one chlorine atom = 7 × 1 = 7
And the total valence electrons = 8 + 1 + 7 = 16
- Second, find the total electron pairs
We have a total of 16 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 = 16 ÷ 2 = 8
- Third, determine the central atom
Here hydrogen can not be 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.
Now we have to choose the central atom from carbon and chlorine. Place the least electronegative atom at the center.
Since carbon is less electronegative than chlorine, assume that the central atom is carbon.
Here, there are two carbon atoms, so we can assume any one as the central atom.
Let’s assume that the central atom is left carbon.
Therefore, place carbons in the center and hydrogen and chlorine on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 8 electron pairs. And three bonds are already marked. So we have to only mark the remaining five 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. Hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell. And chlorine is a period 3 element, so it can keep more than 8 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are chlorine, hydrogen, and right carbon. But no need to mark on hydrogen, because hydrogen already has two electrons.
So for chlorine, there are three lone pairs, for right carbon, there are two lone pairs, and for left carbon, there is zero lone pair because all five electron pairs are over.
Mark the lone pairs on the sketch as follows:
#3 Mark Charges
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 – 0 – ½ (4) = +2
For right carbon atom, formal charge = 4 – 4 – ½ (4) = -2
For hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For chlorine atom, formal charge = 7 – 6 – ½ (2) = 0
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
Convert a lone pair of the right carbon atom to make a new C — C bond with the left carbon atom as follows:
#5 Minimize Charges Again
Since there are charges on both carbon atoms, again 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) forms an octet. Hence, the octet rule is satisfied.
Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of C2HCl.
Next: AlF3 Lewis Structure