Lewis Structure of HNO3 (With 6 Simple Steps to Draw!)

I’m super excited to teach you the lewis structure of HNO3 in just 6 simple steps.

Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of HNO3 molecule.

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of HNO3 (Nitric acid) contains one double bond between the Nitrogen atom (N) & one Oxygen atom (O) and the rest other atoms are single bonded with each other. The nitrogen atom is at the center and it is surrounded by 2 oxygen atoms and one O-H bond.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of HNO3).

6 Steps to Draw the Lewis Structure of HNO3

Step #1: Calculate the total number of valence electrons

Here, the given molecule is HNO3. In order to draw the lewis structure of HNO3, first of all you have to find the total number of valence electrons present in the HNO3 molecule.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in HNO3

• For Hydrogen: 

Hydrogen is a group 1 element on the periodic table. ^[1]

Hence, the valence electron present in hydrogen is 1 (see below image).

• For Nitrogen:

Nitrogen is a group 15 element on the periodic table. ^[2]

Hence, the valence electrons present in nitrogen is 5 (see below image).

• For Oxygen:

Oxygen is a group 16 element on the periodic table. ^[3]

Hence, the valence electron present in oxygen is also 6 (see below image).

Hence in a HNO3 molecule, 

Valence electrons given by Hydrogen (H) atom = 1
Valence electrons given by Nitrogen (N) atom = 5
Valence electrons given by each Oxygen (O) atom = 6
So, total number of Valence electrons in HNO3 molecule = 1 + 5 + 6(3) = 24

Step #2: Select the center atom

While selecting the atom, always put the least electronegative atom at the center. 

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[4]

Here in the HNO3 molecule, if we compare the nitrogen atom (N), oxygen atom (O) and hydrogen atom (H), then hydrogen is less electronegative than nitrogen and oxygen. But as per the rule, we have to keep hydrogen outside.

So, nitrogen (which is less electronegative than oxygen) should be placed in the center and the remaining oxygen atoms as well as OH group will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of HNO3 molecule, put the two electrons (i.e electron pair) between the nitrogen-oxygen atoms and oxygen-hydrogen atoms to represent a chemical bond between them.

These pairs of electrons present between the Nitrogen-Oxygen atoms as well as between the Oxygen & Hydrogen atoms form a chemical bond, which bonds these atoms with each other in a HNO3 molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of HNO3, the outer atoms are hydrogen atom as well as oxygen atom.

Hydrogen already has a duplet (see below image).

So now, you have to complete the octet on oxygen atom (because oxygen requires 8 electrons to have a complete outer shell).

Now, you can see in the above image that the oxygen atom forms an octet.

Also, all the 24 valence electrons of HNO3 molecule (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of HNO3.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e nitrogen) has an octet or not. 

In simple words, we have to check whether the central Nitrogen (N) atom has 8 electrons or not.

As you can see from the above image, the central atom (i.e nitrogen) has only 6 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of nitrogen atom, we have to move the electron pair from the outer atom (i.e oxygen atom) to form a double bond.

Now you can see from the above image that the central atom (i.e nitrogen), is having 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on oxygen atom (O), nitrogen atom (N) as well as each hydrogen atom (H).

For that, you need to remember the formula of formal charge;

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

• For Hydrogen:
  Valence electron = 1 (as it is in group 1)
  Nonbonding electrons = 0
  Bonding electrons = 2
• For Nitrogen:
  Valence electrons = 5 (as it is in group 15)
  Nonbonding electrons = 0
  Bonding electrons = 8
• For double bonded Oxygen:
  Valence electrons = 6 (as it is in group 16)
  Nonbonding electrons = 4
  Bonding electrons = 4
• For single bonded oxygen (left):
  Valence electron = 6 (as it is in group 16)
  Nonbonding electrons = 4
  Bonding electrons = 4
• For single bonded oxygen (right):
  Valence electron = 6 (as it is in group 16)
  Nonbonding electrons = 6
  Bonding electrons = 2

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

Let’s keep these charges on the atoms in the above lewis structure of HNO3 molecule.

As you can see in the above sketch, there are still +1 and -1 charges on the Nitrogen atom and Oxygen atom respectively. The pair of positive and negative charges gets canceled. And this is the most stable lewis structure of HNO3.

Each electron pair (:) in the lewis dot structure of HNO3 represents the single bond ( | ). So the above lewis dot structure of HNO3 can also be represented as shown below.

(Note: In step 5, if we had moved the electron pair from the oxygen of OH group, then there will be another +1 and -1 charges on these oxygen atoms. So there will be total 4 charges. But in order to get the most stable lewis structure, here we move the electron pair from the oxygen atom which is not from the OH group.)

Related lewis structures for your practice:
Lewis structure of SCN-
Lewis structure of ClF3
Lewis structure of Cl2
Lewis structure of HF
Lewis structure of SCl2

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