Lewis Structure of HNO2 (With 6 Simple Steps to Draw!)

Ready to learn how to draw the lewis structure of HNO2?

Awesome!

Here, I have explained 6 simple steps to draw the lewis dot structure of HNO2 (along with images).

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

Lewis structure of HNO2 (Nitrous 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 1 oxygen atom 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 HNO2).

6 Steps to Draw the Lewis Structure of HNO2

Step #1: Calculate the total number of valence electrons

Here, the given molecule is HNO2. In order to draw the lewis structure of HNO2, first of all you have to find the total number of valence electrons present in the HNO2 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 HNO2

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 6 (see below image).

Hence in a HNO2 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 HNO2 molecule = 1 + 5 + 6(2) = 18

Step #2: Select the center atom (H is always outside)

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 HNO2 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 oxygen atom 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 HNO2 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 HNO2 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 HNO2, 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, only 16 valence electrons of HNO2 molecule are used in the above structure.

But there are total 18 valence electrons in HNO2 molecule (as calculated in step #1).

So the number of electrons left to be kept on the central atom = 18 – 16 = 2.

So let’s keep these two electrons (i.e 1 electron pair) on the central atom.

Now, 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 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 = 2
Bonding electrons = 6
For double bonded Oxygen:
Valence electrons = 6 (as it is in group 16)
Nonbonding electrons = 4
Bonding electrons = 4
For single bonded Oxygen:
Valence electron = 6 (as it is in group 16)
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
H	=	1	–	0	–	2/2	=	0
N	=	5	–	2	–	6/2	=	0
Double bonded O	=	6	–	4	–	4/2	=	0
Single bonded O	=	6	–	4	–	4/2	=	0

So you can see above that the formal charges on hydrogen, nitrogen as well as oxygen are “zero”.

Hence, there will not be any change in the above structure and the above lewis structure of HNO2 is the final stable structure only.

Each electron pair (:) in the lewis dot structure of HNO2 represents the single bond ( | ). So the above lewis dot structure of HNO2 can also be represented as shown below.

Article by;

Jay Rana

Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. With a desire to make learning accessible for everyone, he founded Knords Learning, an online learning platform that provides students with easily understandable explanations. Read more about our Editorial process.

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