HNO2 Lewis structure

HNO₂ (nitrous acid) has one hydrogen atom, one nitrogen atom, and two oxygen atoms.

In the HNO₂ Lewis structure, there is one single bond and one double bond around the nitrogen atom, with two oxygen atoms attached to it, and on each oxygen atom, there are two lone pairs. And the oxygen atom having a single bond is attached with one hydrogen atom.

Alternative method: Lewis structure of HNO₂

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, hydrogen lies in group 1, nitrogen lies in group 15, and oxygen lies in group 16.

Hence, hydrogen has one valence electron, nitrogen has five valence electrons, and oxygen has six valence electrons.

Since HNO₂ has one hydrogen atom, one nitrogen atom, and two oxygen atoms, so…

Valence electrons of one hydrogen atom = 1 × 1 = 1
Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of two oxygen atoms = 6 × 2 = 12

And the total valence electrons = 1 + 5 + 12 = 18

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

• Second, find the total electron pairs

We have a total of 18 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 = 18 ÷ 2 = 9

• 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 nitrogen and oxygen. Place the least electronegative atom at the center.

Since nitrogen is less electronegative than oxygen, assume that the central atom is nitrogen.

Therefore, place nitrogen in the center and hydrogen and oxygen on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 9 electron pairs. And three bonds are already marked. So we have to only mark the remaining six 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. And both (nitrogen and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogen and oxygens. But no need to mark on hydrogen, because hydrogen already has two electrons.

So for left oxygen, there are two lone pairs, for right oxygen, there are three lone pairs, and for nitrogen, there is one lone pair.

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 – 2 – ½ (2) = 0

For nitrogen atom, formal charge = 5 – 2 – ½ (4) = +1

For left oxygen atom, formal charge = 6 – 4 – ½ (4) = 0

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

Here, both nitrogen and oxygen atoms have charges, so mark them on the sketch as follows:

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

Convert a lone pair of the right oxygen atom to make a new N — O bond with the nitrogen atom as follows:

Final structure

The final structure of HNO₂ features a central nitrogen atom connected to one oxygen atom via a double bond and to another oxygen atom via a single bond, with the latter oxygen also bonded to a hydrogen atom. In this configuration, the nitrogen atom satisfies the octet rule by maintaining one lone pair alongside its three bonding pairs. The double-bonded oxygen atom fulfills its octet by retaining two lone pairs, while the hydroxyl oxygen (bonded to hydrogen) also carries two lone pairs. This arrangement is the most stable because it results in formal charges of zero for every atom in the molecule, representing the most energetically favorable state. Therefore, this specific electronic distribution serves as the definitive and most accurate Lewis representation of nitrous acid.

Next: ICl₂^– Lewis structure

External video

• HNO2 Lewis Structure: How to Draw the Lewis Structure for Nitrous Acid – YouTube • Wayne Breslyn

External links

• https://www.chemistryscl.com/general/hno2-lewis-structure/
• https://techiescientist.com/hno2-lewis-structure/
• https://geometryofmolecules.com/hno2-lewis-structure-molecular-geometry-hybridization-bond-angle-and-shape/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/HNO2-lewis-structure.html
• https://lambdageeks.com/hno2-lewis-structure/