HClO2 Lewis structure

HClO₂ (chlorous acid) has one hydrogen atom, one chlorine atom, and two oxygen atoms.

In the HClO₂ Lewis structure, 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.

Alternative method: Lewis structure of HClO₂

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, hydrogen lies in group 1, chlorine lies in group 17, and oxygen lies in group 16.

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

Learn how to find: Hydrogen valence electrons, Chlorine valence electrons, and Oxygen valence electrons

• 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

Lone pair

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:

Formal charge

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.

Convert a lone pair of the top oxygen atom to make a new Cl — O bond with the chlorine atom as follows:

Final structure

The final structure of HClO₂ consists of a central chlorine atom connected to two oxygen atoms, one of which is further bonded to a hydrogen atom. In this arrangement, the chlorine atom utilizes an expanded valence shell to form a double bond with one lone oxygen atom and a single bond with the hydroxyl (-OH) group. Additionally, the chlorine atom maintains two lone pairs to complete its electronic configuration. All atoms in this structure—the chlorine, the hydrogen, and both oxygens—carry a formal charge of zero, which represents the most stable and energetically favorable state for the molecule. The double-bonded oxygen atom fulfills its octet with two lone pairs, while the hydroxyl oxygen atom retains two lone pairs alongside its two single bonds. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of chlorous acid.

Next: CH₂NH Lewis structure

External video

• How to Draw the Lewis Structure for HClO2: Chlorous Acid – YouTube • Wayne Breslyn

External links

• https://lambdageeks.com/hclo2-lewis-structure/