CNO- Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

CNO- (Fulminate ion) lewis structure has a Nitrogen atom (N) at the center which is surrounded by Carbon atom (C) and Oxygen atom (O). There is a single bond between the Nitrogen (N) & Oxygen (O) atom and a triple bond between the Carbon (C) & Nitrogen (N).

If you haven’t understood anything from the above image of CNO- ion (fulminate ion) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of CNO- ion.

So let’s move to the steps of drawing the lewis structure of CNO- ion.

Steps of drawing CNO- lewis structure

Step 1: Find the total valence electrons in CNO- molecule

In order to find the total valence electrons in an CNO- (fulminate ion) ion, first of all you should know the valence electrons present in carbon atom, nitrogen atom as well as oxygen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of carbon, nitrogen as well as oxygen using a periodic table.

Total valence electrons in CNO- ion

→ Valence electrons given by carbon atom:

Carbon is group 14 element on the periodic table. ^[1] Hence the valence electrons present in carbon is 4.

You can see the 4 valence electrons present in the carbon atom as shown in the above image.

→ Valence electrons given by nitrogen atom:

Nitrogen is a group 15 element on the periodic table. ^[2] Hence the valence electrons present in nitrogen is 5.

You can see the 5 valence electrons present in the nitrogen atom as shown in the above image.

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. ^[3] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

Hence, 

Total valence electrons in CNO- ion = valence electrons given by 1 carbon atom + valence electrons given by 1 nitrogen atom + valence electrons given by 1 oxygen atom + 1 more electron is added due to 1 negative charge = 4 + 5 + 6 + 1 = 16.

Step 2: Prepare a rough sketch

To draw the rough sketch of CNO, just look at its chemical formula only. You can see that there is a nitrogen atom (N) at the center and it is surrounded by carbon atom as well as oxygen atom on both sides.

So let’s draw a rough sketch for the same.

Step 3: Connect each atoms by putting an electron pair between them

Now in the CNO molecule, you have to put the electron pairs between the carbon atom (C), nitrogen atom (N) and oxygen atom (O).

This indicates that the carbon atom (C), nitrogen atom (N) and oxygen atom (O) are chemically bonded with each other in a CNO molecule.

Step 4: Make the outer atoms stable

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of CNO molecule, you can see that the outer atoms are carbon atom and oxygen atom.

These outer carbon and oxygen atoms are forming an octet and hence they are stable.

Also, in step 1 we have calculated the total number of valence electrons present in the CNO- ion.

The CNO- ion has a total 16 valence electrons and all these valence electrons are used in the above sketch.

Hence there are no remaining electron pairs to be kept on the central atom.

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom. If it does not have octet, then shift the lone pair to form a double bond or triple bond.

In this step, you have to check whether the central nitrogen atom (N) is stable or not.

In order to check the stability of the central nitrogen (N) atom, we have to check whether it is forming an octet or not.

Unfortunately, the nitrogen atom is not forming an octet here. Nitrogen has only 4 electrons and it is unstable.

Now to make this nitrogen atom stable, you have to shift the electron pair from the outer carbon atom so that the nitrogen atom can have 8 electrons (i.e octet).

(Note: Remember that you have to shift the electron pair from the atom which is less electronegative.
This is because the less electronegative atom has more tendency to donate the electron.
Here if we compare the carbon atom and oxygen atom, then the carbon atom is less electronegative.
So you have to shift the electron pair from the carbon atom.)

But after shifting one electron pair, the nitrogen atom is still not forming an octet as it has only 6 electrons. 

So again we have to shift one more electron pair from the carbon atom only. (Because carbon is less electronegative than oxygen.)

After shifting this electron pair, the central nitrogen atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that the nitrogen atom is forming an octet.

And hence the nitrogen atom is stable.

Now let’s proceed to the final step to check whether the lewis structure of CNO is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of CNO molecule.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on carbon (C), nitrogen (N) atom as well as oxygen (O) atoms present in the CNO molecule.

For calculating the formal charge, you have to use the following formula;

Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons

You can see the number of bonding electrons and nonbonding electrons for each atom of CNO molecule in the image given below.

For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 6
Nonbonding electrons = 2

For Nitrogen (N) atom:
Valence electrons = 5 (because nitrogen is in group 15)
Bonding electrons = 8
Nonbonding electrons = 0

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
C	=	4	–	6/2	–	2	=	+1
N	=	5	–	8/2	–	0	=	0
O	=	6	–	2/2	–	6	=	-1

From the above calculations of formal charge, you can see that the carbon (C) atom has -1 charge, and the oxygen (O) atom has +1 charge.

So let’s keep these charges on the respective atoms in the CNO molecule.

The +1 and -1 charge gets canceled and so the overall -1 charge on the CNO molecule is represented in the image given below.

In the above lewis dot structure of CNO- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of CNO- ion.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

BrO2- Lewis Structure	N2O4 Lewis Structure
COF2 Lewis Structure	SCl4 Lewis Structure
PBr5 Lewis Structure	SiS2 Lewis Structure