HNO2 Lewis Structure, Characteristics:19 Facts You Should Know

In this article, we learn about the HNO2 lewis structure and many more characteristic features in detail.

HNO2 lewis structure or Nitrous acid is an inorganic covalent molecule. HNO2 lewis structure is although moderate acid in aqueous solution it behaves as strong acid.. the central N atom in the nitrous acid is sp2 hybridized but the geometry around the central N is bent. The conjugate base of nitrous acid nitrite is highly resonance stabilized and for this reason, the acid is strong.

In the Nitrous acid, there is a double bond present between N and O, and another O is a single bond with central N, and H is attached with one of the O atoms which makes a single bond with N. The conjugate compound of Nitrous acid is nitrous oxide which is known as laughing gas.

Some facts about HNO2

The physical state of the HNO2 lewis structure is liquid. The color of the HNO2 is pale blue. Nitrous acid has a molar mass value is 47.013 g/mol. The density of the HNO2 lewis structure is 1g/mL.

Nitrous acid can be prepared by dissolving dinitrogen trioxide.

N2O3 + H2O = 2HNO2

1.    How to draw the HNO2 lewis structure?

HNO2 lewis structure consists of two O, one N, and one H atoms. The HNO2 lewis structure helps us to find different covalent characteristics of the nitrous acid.

There are a few many steps we have to follow for drawing the HNO2 lewis structure.

First of all, we should count the valence electrons for the HNO2 lewis structure drawing. Here we only calculate the valence electrons for every substituent present in the HNO2 lewis structure then and added them together.

The valence electrons for N, O, and H atoms are 5,6, and 1 respectively. As they are group VA, VIA, and IA elements. So, the valence electrons present in the HNO2 lewis structure are  5+(2*6)+1 = 18 electrons.

Now in the 2nd step, we have to choose the atom which will be the central atom for the HNO2 lewis structure. The size of N is larger than O and H atoms, and also the electronegativity of N is lesser than O, so we have to consider N as the central atom for the HNO2 lewis structure.

In the 3rd step, we have to check all the atoms should obey the octet rule for stabilization. According to the octet rule s block element should contain two electrons in the valence shell and the p block element should contain eight electrons in their valence shell respectively. H is the s block element whereas O and N are the p block elements.

So, the electrons should be required according to the octet rule in the HNO2 lewis structure, (8*3) +2 = 26 electrons. but the valence electrons for the HNO2 lewis structure are lesser than the electrons needed. So, the required number of electrons 26-18 = 8 electrons should be accumulated by the 8/2 = 4 bonds.

Now we should the 4 bonds in the HNO2 lewis structure to connect all the atoms to the central atom. But H is attached to the O atom in the HNO2 lewis structure.

In the last step, we should check all the valency of atoms should be satisfied after the required number of bonds is added. We add multiple bonds if necessary.

We add a double bond between O and N atoms. We also added lone pairs over the N and O atoms after the bond formation to get a clear picture of the HNO2 lewis structure.

2.      HNO2 lewis structure shape

The HNO2 lewis structure shape depends according to the VSEPR theory. The AX2 type molecule having lone pair over the central atom is always adopted a trigonal pyramidal structure but if there any deviation factor is present then it changes its geometry.

HNO2 Shape

According to the VSEPR (Valence Shell Electrons Pair Repulsion) theory, the molecule AX2 type having lone pair over the central atom should be adopted a trigonal pyramidal structure. But in the HNO2 lewis structure, there is a double is present between N and O atoms, and N and O both contain lone pairs.

So, there is massive bond pair- lone pairs repulsion occurs and due to minimizing this repulsion, the central tom rearranges the geometry to a bent shape. There is a deviation factor is present so the geometry of the HNO2 also deviated from the original one.

3.    HNO2 valence electrons

The valence electrons for the HNO2 lewis structure are the summation of the individual atom’s valence electrons which are present in the HNO2.

The central atom of the HNO2 lewis structure is N which is a group VA element and it has five valence electrons in its valence shell. The other important atom O is a group 16th  element and that’s why it has six valence electrons in its outermost orbital that is 2s and 2p orbitals.

We all know H has only one electron. So, total valence electrons for the HNO2 lewis structure is the summation of the individual atoms and the value is, 1+(6*2)+5 =18 electrons.

4.    HNO2 lewis structure lone pairs

In the HNO2 lewis structure, N, as well as O, contains the lone pairs. Because only N and O have the excess valence electrons after the bond formation

N has five electrons in the valence orbital and the stable valency of N is three. So, after the formation of three successive bond pairs, it has two electrons in its valence orbital and they exist as lone pair.

O has sis electrons in its valence shell and O is divalent, so after the formation of the two successive bond pairs, it also contains two lone pairs as well.

H is a lack of lone pair in the HNO2 lewis structure.

5.    HNO2 lewis structure octet rule

Every covalent molecule obeys the octet rule for gaining stability by completing its valence shell. Every atom in the HNO2 lewis structure should obey the octet rule.

H is s block element having electronic configuration 1s1 and its valence orbital is s. According to the octet rule s block element should fulfill their s orbital by two electrons as s orbital contains a maximum of two electrons by Hund’s rule of multiplicity.

 H shares its one electron with one electron of O to form a stable covalent bond. Now H has two electrons in its valence orbital by sharing a bond and completing its octet.

The p block element should complete its valence shell by six electrons as the p orbital can contain a maximum of six electrons because it has three sub-shells and the s orbital contains two electrons as it has only one sub-shell.

The electronic configuration of N and O are [He]2s22p3 and [He]2s22p4. So, from the electronic configuration, we can say to complete the octet needs three more electrons and O needs two more electrons in the valence shell respectively.

In the HNO2 lewis structure, N formed three bonds, two sigma bonds, and one π bond by using three electrons from its p orbital. One bond share two electrons and three bonds share six electrons, so that way the p orbital of N is fulfilled and it completes its octet.

O formed two bonds, one O formed one sigma and one π bond, and another O formed two sigma bonds. So, four electrons will be accumulated by the two sigma bonds, and O used two electrons from its p orbital for bond formation and the rest of the four electrons exist as lone pairs. So, O also complete its octet in the HNO2 lewis structure.

6.    HNO2 lewis structure formal charge

The formal charge of the HNO2 lewis structure is calculated to check any kind of charge appearance in the molecule. It is a hypothetical concept by considering the same electronegativity for every atom in the HNO2 lewis structure.

The formula we can use to calculate the formal charge, F.C. = Nv – Nl.p. -1/2 Nb.p.

Where Nv is the number of electrons in the valence shell or outermost orbital, Nl.p is the number of electrons in the lone pair, and Nb.p  is the total number of electrons that are involved in the bond formation only.

The formal charge of N is, 5-2-(6/2) = 0

The formal charge of O is, 6-4-(4/2) = 0

The formal charge of H is, 1-0-(2/2) = 0

The overall formal charge of HNO2 is zero, so we can conclude that HNO2 lewis structure is neutral.

7.    HNO2 lewis structure angle

The bond angle is variable concerning N and O atoms in the HNO2 lewis structure. The geometry is different around O and N atoms.

HNO2 Bond Angle

The hybridization around the central N is sp2 and the best angle for sp2 hybridized molecule is 1200 if they adopt trigonal planar geometry. But due to steric repulsion, the molecule changes its shape and changes its bond angle as well.

To avoid repulsion, the bond angle around the central N is also decreased from its original value to 1100. The other bond angle around the O atom is like a water molecule and the bond angle is 1020 due to the presence of two pairs of lone pairs.

8.    HNO2 lewis structure resonance

There are different canonical Skelton forms of HNO2 lewis structures present where electron clouds delocalization can occur.

HNO2 Resonating Structures

The structure I is more stable than structure II because both molecules contain the same number of covalent bonds but in structure II the positive charge is on the electronegative O atom, which is the destabilization factor.

9.    HNO2 hybridization

The central N atom in the HNO2 lewis structure is sp2 hybridized.

The hybridization of N is calculated by the following formula,

H = 0.5(V+M-C+A), where H= hybridization value, V is the number of valence electrons in the central atom, M = monovalent atoms surrounded, C=no. of cation, A=no. of the anion.

So, the hybridization of N is, ½(5+1) = 3(sp2)

Structure           Hybridization value  State of hybridization of central atom             Bond angle
Linear           2sp /sd / pd         1800
Planner trigonal  3sp2     1200
Tetrahedral        4sd3/ sp3       109.50
Trigonal bipyramidal  5sp3d/dsp3                      900 (axial), 1200(equatorial)
Octahedral        6sp3d2/ d2sp3        900
Pentagonal bipyramidal7sp3d3/d3sp3       900,720

If the number of hybrid orbitals involved in hybridization is 3 then it should be sp2 hybridized.

HNO2 Hybridization

From the box diagram of central N, we can say that we only consider the sigma bond in hybridization, not π bonds or any other multiple bonds, but we also consider the lone pairs also as they exist in the valence shell so lone pairs always participate in the hybridization.

10.  Is HNO2 polar or nonpolar?

HNO2 is a polar molecule.

The shape of the molecule is asymmetric so there is no chance for canceling out of dipole-moment and there is a resultant dipole-moment present, making the molecule polar.

11.  HNO2 solubility

HNO2 is soluble in the following solvents,

  • Stable esters
  • CCl4
  • Water
  • Benzene

12.  Is HNO2 soluble in water?

Yes, HNO2 is soluble in water

As we know “like dissolves like” and being a polar molecule HNO2 is soluble in water like a polar solvent.


HNO2 is a moderate strong inorganic acid, which conjugate base is quite stable and the conjugate compound acts as laughing gas.

Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.

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