Lewis Structure for NO2 | Nitrogen dioxide Oxidation number

Lewis structure of NO2 (Nitrogen dioxide) is drawn in this tutorial step by step. You can learn basics of how to draw a lewis structure properly from this example.


This is a special case of lewis structure drawing because, there is a unpaired electron in the valance electrons. You will see this case when we draw the lewis structure of NO2 in next sections.



Steps of drawing NO2 lewis structure

Following steps are required to draw the NO2 lewis structure and they are explained in detail in this tutorial.

  1. Find total number of electrons of the valance shells of nitrogen and oxygen atoms
  2. Total electrons pairs
  3. Center atom selection
  4. Put lone pairs on atoms
  5. Check the stability and minimize charges on atoms by converting lone pairs to bonds.

Drawing correct lewis structure is important to draw resonance structures.



Total number of electrons of the valance shells of nitrogen and oxygen atoms

Nitrogen and oxygen are located at VA and VIA groups respectively in the periodic table. So nitrogen has five electrons in its valence shell. In oxygen atom, there are six electrons in its valence shell.


  • Total valence electrons given by nitrogen atom = 5

There are two oxygen atoms in NO2, Therefore

  • Total valence electrons given by oxygen atoms = 6 *2 = 12

  • Total valence electrons = 5 + 12 = 17


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, NO2, Total pairs of electrons are 8 and one electron exists as unpaired electron because 17 cannot be divided exactly by 2.



Center atom of NO2

To be the center atom, ability of having greater valance is important. Therefore nitrogen has the more chance to be the center atom (See the figure). So, now we can build a sketch of NO2.

center atom of NO2

Lone pairs on atoms

There are already two N-O bonds in the sketch. Therefore only six valence electrons pairs are remaining.

Mark those six valence electrons pairs as lone pairs in outside atoms (on oxygen atoms). One oxygen atom will take three lone pairs following the octal rule (oxygen and nitrogen atoms cannot keep more than eight electrons in their valence shells).

Mark unpaired electron on nitrogen atom.

unstable lewis structure of NO2

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

The drawn structure is not a stable one because both oxygen atoms and nitrogen atoms have charges. Also nitrogen has a +2 charge and it decreases the stability of that structure.

Now, we should try to minimize charges by converting lone pair(s) which exist on oxygen atoms to bonds. So convert one lone pair of one oxygen atom to a N-H bond.

Now there is a double bond between nitrogen and one oxygen atom. There is a single bond also with nitrogen atom and other oxygen atom.


lewis structure for NO2

In new structure, charges of atoms reduced than previous structure. Now there is no any charge on one oxygen atom. Charge of nitrogen atom is also decreased to +1 from +2. Now you understand this structure of NO2 is more stable than previous structure. So, this structure has more chance to be the lewis structure of NO2.


We cannot convert more lone pairs of other oxygen atom to make a bond with nitrogen atom because a nitrogen atom cannot keep more than eight electrons in its valence shell.




NO2 structure

The bond length between the nitrogen atom and the oxygen atom is 119.7 pm. That means both bonds exist between oxygen and nitrogen are same.

Due to exist of unpaired electron, NO2 is a free radical.



There is a unpaired electron on nitrogen atom in NO2 lewis structure. Cannot it be shifted to an oxygen atom?

In above lewis structure, octal of oxygen atoms are already completed. There is no chance to have more than eight electrons in last shell.



Effect of unpaired electron

NO2 is a free radical. When it is in the presence of sun light, reacts with oxygen gas and produce NO and atomic oxygen. This is an initial step of photochemical smog which is occurred at cities which have high traffics.



Oxidation number of NO2

Oxygen is more electronegative than nitrogen. Therefore electrons of bonds are attracted towards oxygen atoms more than nitrogen.

oxidation number of nitrogen in NO2

There are three bonds between (two σ + one π) nitrogen atom and oxygen atoms. De to those bonds, nitrogen partially loses its three electron. So due to that case, nitrogen gets +3 oxidation state. But, wait. When your consider last shell of nitrogen atom, nitrogen belongs only four electrons. So nitrogen atom is lacking one electron and it makes +1 oxidation number. At finally, overall oxidation number of nitrogen is +4 (+3 + 1).




Questions

Ask your chemistry questions and find the answers

What is the colour of NO2? I have heard that it is brown colour. Is it true. Why NO2 has a colour?

At room temperature, nitrogen dioxide is a brown colour gas. In lewis structure of NO2, there is a unpaired electron on nitrogen atom. That unpaired electron is the reason for showing colours by NO2 molecule.


NO2 structure?

There is an unpaired electron on nitrogen atom. Therefore the molecule has three electron pairs around nitrogen atom and is trigonal planar for electron pair geometry. The one lone electron exerts a less repulsion than normal on the two bonding oxygen atoms so they are able to spread out more to a 1340 bond angle from the ideal of 1200.



What is the difference of lewis structures of NO2 and NO2-

In the lewis structure of NO2, there is a unpaired electrons on nitrogen atom. But in the NO2- lewis structure, there is lone pair on nitrogen atom.