Molecular Geometry, Hybridization, and Polarity of HNO2 Lewis Structure

Monoprotic acids include HNO2, often known as nitrous acid (acids that donate one proton during dissociation). It’s a weak acid that only exists in the form of nitrite salts in solution (NO2-).

The oxygen content of nitrous acid is lower than that of nitric acid (HNO3). Scheele found it, which is quite unstable in nature. It has a strong stench and looks as a light blue liquid.

Acidification of sodium nitrite and mineral acid produces nitrous acid. The product HNO2 is created in the reaction mixture itself, which is normally done at ice temperatures.

Dinitrogen trioxide can also be made by dissolving it in water. The following is the reaction:

N2O3    +    H2O     ——>      2HNO2

Lewis Structure of HNO2

Making a Lewis structure is the first and most important step in determining numerous features connected to a molecule’s bonding.

As a result, whenever bonding is described in the context of a molecule or a compound, your mind should automatically leap to the Lewis structure of the substance in question.

There are a few things to keep in mind before we start building the Lewis structure for HNO2.

The Lewis structure represents the number of valence electrons in an atom. The number written on top of a group’s column in a periodic table can be used to identify the number of valence electrons in that group. Around the atom, the valence electrons are depicted as dots.

These electrons are positioned so that each atom’s octet is complete. This essentially means that each atom should have 8 electrons surrounding it in order to establish stability.

Only hydrogen and helium are exceptions, as they have two electrons in their outermost shell and hence follow the duplet rule.

Let’s look at the steps involved in creating a Lewis diagram:-

Step 1: We start by counting the molecule’s total number of valence electrons.

When we look at HNO2, we can see that it has one valence electron, five valence electrons, and six valence electrons, with two atoms of O, for a total of 62 = 12 valence electrons.

As a result, the total number of valence electrons is 1+5+12 = 18 valence electrons when we add everything up.

Step 2: Now we’ll look at the second step, which is determining the compound’s core atom (one which has the highest number of bonding sites).

In the instance of HNO2, it’s important to remember that anytime H is connected to a polyatomic molecule (in this example, NO2), it’s always to one of the oxygen atoms.

As a result, the core atom is N, which has the most bonding sites and is less electronegative than O.

Step 3: To simulate a chemical link, we now place two valence electrons between each atom.

Step 4: We now arrange the remaining valence electrons so that each atom achieves its octet or duplet (H).

Step 5. If the atoms do not attain their octet form after arranging these electrons, we convert the valence electrons into a double or triple bond so that each atom has its complete octet.

As a final step, you can look at each atom’s formal charge. It should be as low as feasible, and the formula below can be used to compute it.

Let’s have a look at HNO2 now.

The total number of valence electrons is equal to 18.

N is the central atom.

We note that N is missing two valence electrons to complete its octet after arranging all 18 valence electrons around the molecule.

As a result, we use one pair of valence electrons from O to establish a double bond with N, completing each atom’s octet. The Lewis structure of HNO2 is now complete, and we can see that the formal charge of each atom is zero.

The procedures outlined above can be used to determine the Lewis structure of any molecule.

Hybridization of HNO2

The Hybridization of a molecule is the next step after learning the Lewis structure. Hybridization is the production of new hybrid orbitals that aid in determining the shape and characteristics of a molecule.

Sp2 is the Hybridization of HNO2.

Hybridisation can be understood in two ways:

  1. We can locate hybridization by comprehending the idea that underpins it. The number of bonds and the lone pair of the central atom are added to define hybridization.

Hybridization’s (H) value is as follows:

It is sp hybridised if H=2.

If H=3, sp2 has been hybridised.

H=4 indicates that it sp3 hybridised.

H=5 indicates that it sp3d hybridised.

H=6 denotes sp3d2 hybridization.

We know that N is the core element in HNO2. It has a lone pair and is linked to two oxygen atoms. As a result, the total (H) is 2+1=3, indicating that it is sp2 hybridised.

  1. We also have a formula that can be used to determine a molecule’s hybridization.

The following is the formula for calculating hybridization:-

H= 1/2[V+M-C+A]

C= Charge on cation or more electropositive atom, H= Hybridization, V= Number of Valence electrons, C= Charge on anion or more electropositive atom, and A= Charge on anion or more electropositive atom.

When we look at HNO2, we may observe that

V is equal to 5. (valence electrons of the central atom N)

M = 1 The atom oxygen (O) is divalent. As a result, it isn’t counted. The only atom that is monovalent is H, which has only one atom.

The charge of a cation or anion will be zero since HNO2 is a neuronal molecule (overall charge is 0).



H=3 indicates that HNO2 has been hybridised with Sp2. As a result, these two approaches can be used to find HNO2 hybridization.

Molecular Geometry of HNO2

The next critical step is to identify HNO2’s molecular shape. It gives us the shape of each atom as well as the bond angles between them.

HNO2 has a bent molecular geometry (a bent-shaped molecule). The bond angles created are nearly 120 degrees.

The AXN notation can be used to identify this, with A representing the central atom, which in this case is N. Assume A=1. The number of atoms linked to the core atom is then represented as X. X=2 is the result (2 Oxygen atoms bonded to Nitrogen).

The non-bonding electrons, or lone pairs, on the centre atom are denoted by the letter N. Because there are two lone pairs on the N atom, N=1. As a result, the notation becomes AX2N.

We can see that HNO2 has a bent form if we look it up in the VSEPR chart below.

Polarity of HNO2

The chemical HNO2 is classified as polar.

Polarity develops when there is an electronegativity mismatch between various atoms inside a molecule. The net dipole moment of polar molecules is zero, hence they have an asymmetrical structure.

We must first draw the Lewis structure of HNO2 in order to determine its polarity. It is obvious from the Lewis structure that HNO2 is not a symmetrical molecule.

N has a single bond with OH on one side and a double bond with O on the other. We may already deduce that HNO2 is a polar molecule from this.

To be certain of this, we examine the molecular geometry of the substance. It is asymmetrical due to the bent shape caused by the lone pair.

We also see that the O at one end of the molecule is extremely electronegative, while the H at the other end is strongly electropositive.

As a result, we have oppositely charged poles on either end of the molecule, and this, together with the asymmetrical form of HNO2, makes it a polar molecule.

HNO2 Characteristics

When it rises in the air, it emits thick vapours due to its great flammability.

HNO2 has a molar mass of 47.013 g/mol.

The density is roughly 1 g/ml.

HNO2 has a boiling point of 82 degrees Celsius.

Nitrous gas is produced when HNO2 reacts with water. Phosphorus and charcoal can be burned with HNO2 in a fuming state.


  1. It is employed in the synthesis of diazonium salts in amines as well as azo dyes (sandmeyer reaction).
  2. In liquid fuel rockets, it acts as a powerful oxidizer. It can also be used to remove sodium azide’s toxicity.


The Lewis structure, hybridization, molecular geometry, and polarity of HNO2 were all discussed in this article. You should now be able to understand the fundamentals of the chemical HNO2.

We hope you found all of the answers you were looking for, and if you have any questions, please feel free to contact me at any time.

Good luck with your studies!

Read more: Molecular Geometry, Hybridization, and Polarity of HCOOH Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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