HNO3 Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

HNO3 (nitric acid) lewis structure has a Nitrogen atom (N) at the center which is surrounded by two Oxygen atoms (O) and one O-H group. There is 1 double bond between the Nitrogen atom (N) & Oxygen atom (O) and the rest other atoms have a single bond.

If you haven’t understood anything from the above image of HNO3 (nitric acid) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of HNO3.

So let’s move to the steps of drawing the lewis structure of HNO3.

Steps of drawing HNO3 lewis structure

Step 1: Find the total valence electrons in HNO3 molecule

In order to find the total valence electrons in a HNO3 molecule, first of all you should know the valence electrons present in hydrogen atom, nitrogen atom as well as oxygen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of hydrogen, nitrogen as well as oxygen using a periodic table.

Total valence electrons in HNO3 molecule

→ Valence electrons given by hydrogen atom:

Hydrogen is group 1 element on the periodic table. ^[1] Hence the valence electron present in hydrogen is 1.

You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.

→ Valence electrons given by nitrogen atom:

Nitrogen is a group 15 element on the periodic table. ^[2] Hence the valence electrons present in nitrogen is 5.

You can see the 5 valence electrons present in the nitrogen atom as shown in the above image.

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. ^[3] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

Hence, 

Total valence electrons in HNO3 molecule = valence electrons given by 1 hydrogen atom + valence electrons given by 1 nitrogen atom + valence electrons given by 3 oxygen atoms = 1 + 5 + 6(3) = 24.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)

Now here the given molecule is HNO3 (nitric acid) and it contains hydrogen atom (H), nitrogen atom (N) and oxygen atoms (O).

So as per the rule we have to keep hydrogen outside.

Now, you can see the electronegativity values of nitrogen atom (N) and oxygen atom (O) in the above periodic table.

If we compare the electronegativity values of nitrogen (N) and oxygen (O) then the nitrogen atom is less electronegative.

So here the nitrogen atom (N) is the center atom and the oxygen atoms (O) are the outside atom.

Step 3: Connect each atoms by putting an electron pair between them

Now in the HNO3 molecule, you have to put the electron pairs between the oxygen (O) & hydrogen (H) atom and between the oxygen (O) & nitrogen (N) atoms.

This indicates that these atoms are chemically bonded with each other in a HNO3 molecule.

Step 4: Make the outer atoms stable

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of HNO3 molecule, you can see that the outer atoms are hydrogen and oxygen atoms.

These hydrogen and oxygen atoms are forming a duplet and octet respectively and hence they are stable.

Also, in step 1 we have calculated the total number of valence electrons present in the HNO3 molecule.

The HNO3 molecule has a total 24 valence electrons and all these valence electrons are used in the above sketch of HNO3.

Hence there are no remaining electron pairs to be kept on the central nitrogen atom. 

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom. If it does not have octet, then shift the lone pair to form a double bond or triple bond.

In this step, you have to check whether the central nitrogen atom (N) is stable or not.

In order to check the stability of the central nitrogen (N) atom, we have to check whether it is forming an octet or not.

Unfortunately, the nitrogen atom is not forming an octet here. Nitrogen has only 6 electrons and it is unstable.

Now to make this nitrogen atom stable, you have to shift the electron pair from the outer oxygen atom so that the nitrogen atom can have 8 electrons (i.e octet).

After shifting this electron pair, the central nitrogen atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that the nitrogen atom is forming an octet as it has 8 electrons.

Now let’s proceed to the final step to check whether the above lewis structure is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of HNO3.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on hydrogen (H) atom, nitrogen (N) atom as well as oxygen (O) atoms present in the HNO3 molecule.

For calculating the formal charge, you have to use the following formula;

Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons

You can see the number of bonding electrons and nonbonding electrons for each atom of HNO3 molecule in the image given below.

For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0

For Nitrogen (N) atom:
Valence electrons = 5 (because nitrogen is in group 15)
Bonding electrons = 8
Nonbonding electrons = 0

For double bonded Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

For single bonded left Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

For single bonded right Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
H	=	1	–	2/2	–	0	=	0
N	=	5	–	8/2	–	0	=	+1
O (double bonded)	=	6	–	4/2	–	4	=	0
O (single bonded, left)	=	6	–	4/2	–	4	=	0
O (single bonded, right)	=	6	–	2/2	–	6	=	-1

From the above calculations of formal charge, you can see that the nitrogen (N) atom has +1 charge while the single bonded oxygen atom (which is on the right side) has -1 charge.

So let’s keep these charges on the respective atoms of the HNO3 molecule.

The +1 and -1 charge from the above sketch gets canceled and the above lewis dot structure of HNO3 is the stable lewis structure.

In the above lewis dot structure of HNO3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of HNO3.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

SCN- lewis structure	ClF3 lewis structure
Cl2 lewis structure	HF lewis structure
SCl2 lewis structure	PF5 lewis structure