HNO3 Lewis structure

HNO₃ (nitric acid) has one hydrogen atom, one nitrogen atom, and three oxygen atoms.

In the HNO₃ Lewis structure, there is one double bond and two single bonds around the nitrogen atom, with three oxygen atoms attached to it. The oxygen atom with a double bond has two lone pairs, the left oxygen atom (with which the hydrogen atom is attached) also has two lone pairs, and the right oxygen atom with a single bond has three lone pairs.

Also, there is a negative (-1) charge on the right oxygen atom, and a positive (+1) charge on the nitrogen atom.

Alternative method: Lewis structure of HNO₃

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 HNO₃ has one hydrogen atom, one nitrogen atom, and three oxygen atoms, so…

Valence electrons of one hydrogen atom = 1 × 1 = 1
Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of three oxygen atoms = 6 × 3 = 18

And the total valence electrons = 1 + 5 + 18 = 24

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 24 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 = 24 ÷ 2 = 12

• 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 12 electron pairs. And four bonds are already marked. So we have to only mark the remaining eight 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 top oxygen and right oxygen, there are three lone pairs, and for left oxygen, 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 nitrogen atom, formal charge = 5 – 0 – ½ (6) = +2

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

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

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 top oxygen atom to make a new N — O bond with the nitrogen atom as follows:

Final structure

The final structure of HNO₃ features a central nitrogen atom connected to three oxygen atoms, one of which is also single-bonded to a hydrogen atom. In this configuration, the nitrogen atom forms a double bond with one oxygen atom and a single bond with each of the other two oxygens to satisfy its octet. Within this layout, the double-bonded oxygen retains two lone pairs, while the oxygen bonded to the hydrogen atom maintains two lone pairs, and the third oxygen atom fulfills its octet with three lone pairs. This arrangement represents the most stable state for the molecule because it results in a formal charge of +1 on the nitrogen and -1 on the single-bonded oxygen (not bonded to H), while all other atoms carry a formal charge of zero. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of nitric acid.

Next: SCN^– Lewis structure

External video

• HNO3 Lewis Structure – How to Draw the Lewis Structure for HNO3 – YouTube • Wayne Breslyn

External links

• https://www.chemistryscl.com/general/lewis-structure-of-HNO3/
• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/HNO3-lewis-structure.html
• https://techiescientist.com/hno3-lewis-structure/
• https://lambdageeks.com/hno3-lewis-structure/