HNO2 (Nitrous acid) Lewis Structure

HNO2 (Nitrous acid) lewis stricture is drawn step by step by using total valence electrons of each element. There are no charges on atoms and one double bond exists between nitrogen and one oxygen atom in the lewis structure of nitrous acid.

written by: Heshan Nipuna, last update: 25/05/2020

Lewis structure of nitrous acid

HNO2 lewis structure

Nitrogen atom is the center atom in HNO2. There are one C=O bond, one C-O bond and one O-H in HNO2 lewis structure.

Steps of drawing lewis structure of HNO3

There are some steps to follow to draw lewis structures. For HNO3 molecule, its lewis structure and those steps are explained in detail in this tutorial.

  1. Find total number of electrons of the valance shells of hydrogen, nitrogen and oxygen atoms
  2. Total electrons pairs as lone pairs and bonds
  3. Center atom selection
  4. mark lone pairs on atoms
  5. Mark charges if there are
  6. Check the stability and minimize charges on atoms by converting lone pairs to bonds.

Important: Drawing correct lewis structure is important to draw resonance structures correctly.

Total number of electrons of the valance shells of HNO2 acid

There are there types of elements; hydrogen, nitrogen and oxygen. Hydrogen is a group IA element and has only one electron in its last shell (valence shell). Nitrogen is located at group VA and has five electrons in its valence shell. Oxygen is a group VIA element in the periodic table and contains six electrons. Now we know how many electrons are includes in valence shells of each atom.

  • valence electrons given by hydrogen atom = 1
  • valence electrons given by nitrogen atom = 5
  • valence electrons given by oxygen atoms = 6*2 = 12

  • Total valence electrons = 1 + 5 + 12 = 18

Total valence electrons pairs

Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells

Total electron pairs are determined by dividing the number total valence electrons by two. For, HNO2 molecule, Total pairs of electrons are 9 in their valence shells.

Center atom of HNO3

To be the center atom, ability of having greater valance is important. Then, from hydrogen, nitrogen and oxygen, which atom has the highest valence? Nitrogen can show valence five which is greater than maximum valence of oxygen's two. hydrogen's only valence is one. Therefore, nitrogen atom should be the center atom of HNO2.

sketch of HNO2

Lone pairs on atoms

After determining the center atom and sketch of HNO2 molecule, we should start to mark lone pairs on atoms.

  • There are already two N-O bonds and one O-H in the drawn sketch structure. Therefore number of total bonds in the sketch is three. Now only six (12-4) valence electrons pairs are remaining to mark on atoms.
  • First, mark those remaining eight valence electrons pairs as lone pairs in outside atoms (on oxygen atoms). Because oxygen atom follow octal rule (oxygen atom cannot keep more than eight electrons in its valence shell) be careful to protect it. Hydrogen atom cannot keep lone pairs because it cannot keep more than two electrons in its valence shell.
  • After marking lone pairs on oxygen atoms, there is one lone pair to mark on nitrogen atom.)
mark valence electrons in HNO2

Charges on atoms

After, marking electron pairs on atoms, we should mark charges of each atom. One oxygen atoms will get a -1 charge and nitrogen atom get a +1 charge.

mark charges on atoms in nitrous acid

Check the stability and minimize charges on atoms by converting lone pairs to bonds

Best lewis structure should have less charges on atoms.

  • Oxygen atoms should hold negative charges because electronegativity of oxygen is higher than nitrogen (If there are negative charges). Otherwise, we can say, ability of holding negative charges is great in oxygen atoms than nitrogen atom.
  • The drawn structure is not a stable one because one oxygen atom and nitrogen atom have charges.
  • Now, we should try to minimize charges by converting lone pair or pairs to bonds. So convert one lone pair of one oxygen atom to make a N-O bond (See the following figure).
  • Now there is a double bond between nitrogen atom and one oxygen atom. Now, there is one single bond between nitrogen atom and other oxygen atom.
reduce charges to obtain best HNO2 lewis structure

In the new structure of HNO2, charges are reduced. Therefore, this is the best lewis structure we can draw for HNO2 molecule.


How nitrous acid lewis structure is different from nitric acid?

In nitric acid molecule, there are three oxygen atoms. But, in nitrous acid, there are only two oxygen atoms. Both molecules have a nitrogen atom and oxygen atom. Therefore, total valence electrons of two molecules are different and their lewis structures are different.

Lewis Structures of Molecules