HClO2 (chlorous acid) has one hydrogen atom, one chlorine atom, and two oxygen atoms. In the lewis structure of HClO2, there is one single bond and one double bond around the chlorine atom, with two oxygen atoms attached to it. The oxygen atom with a single bond is attached with one hydrogen atom, on both oxygen and chlorine atoms, there are two lone pairs.
Here’s how you can draw the HClO2 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, hydrogen has one valence electron, chlorine has seven valence electrons, and oxygen has six valence electrons.
Since HClO2 has one hydrogen atom, one chlorine atom, and two oxygen atoms, so…
Valence electrons of one hydrogen atom = 1 × 1 = 1
Valence electrons of one chlorine atom = 7 × 1 = 7
Valence electrons of two oxygen atoms = 6 × 2 = 12
And the total valence electrons = 1 + 7 + 12 = 20
- Second, find the total electron pairs
We have a total of 20 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 = 20 ÷ 2 = 10
- 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 chlorine and oxygen. Place the least electronegative atom at the center.
Since chlorine is less electronegative than oxygen, assume that the central atom is chlorine.
Therefore, place chlorine in the center and hydrogen and oxygen on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 10 electron pairs. And three bonds are already marked. So we have to only mark the remaining seven electron pairs as lone pairs on the sketch.
Also remember that hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell. Chlorine is a period 3 element, so it can keep more than 8 electrons in its last shell. And oxygen 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 atoms are oxygens and hydrogen. But no need to mark on hydrogen, because hydrogen already has two electrons.
So for top oxygen, there are three lone pairs, for bottom oxygen, there are two lone pairs, and for chlorine, there are two lone pairs.
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 hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For chlorine atom, formal charge = 7 – 4 – ½ (4) = +1
For top oxygen atom, formal charge = 6 – 6 – ½ (2) = -1
For bottom oxygen atom, formal charge = 6 – 4 – ½ (4) = 0
Here, both chlorine and oxygen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both chlorine and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the top oxygen atom to make a new Cl — O bond with the chlorine atom as follows:
In the above structure, you can see that the central atom (chlorine) 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 HClO2.
Next: CH2NH Lewis Structure