Lewis Structure of CNO- (With 6 Simple Steps to Draw!)

I’m super excited to teach you the lewis structure of CNO- ion in just 6 simple steps.

Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of CNO- ion.

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of CNO- (or Fulminate ion) has a triple bond between the Carbon-Nitrogen atom and a single bond between the Nitrogen-Oxygen atom. The Nitrogen atom (N) is at the center and it is surrounded by Carbon and Oxygen atoms. The Carbon atom has 1 lone pair and the Oxygen atom has 3 lone pairs.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of CNO- ion).

6 Steps to Draw the Lewis Structure of CNO- ion

Step #1: Calculate the total number of valence electrons

Here, the given ion is CNO- ion (fulminate ion). In order to draw the lewis structure of CNO- ion, first of all you have to find the total number of valence electrons present in the CNO- ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in CNO- ion

• For Carbon:

Carbon is a group 14 element on the periodic table. ^[1]

Hence, the valence electrons present in carbon is 4 (see below image).

• For Nitrogen:

Nitrogen is a group 15 element on the periodic table. ^[2]

Hence, the valence electrons present in nitrogen is 5 (see below image).

• For Oxygen:

Oxygen is a group 16 element on the periodic table. ^[3]

Hence, the valence electron present in oxygen is 6 (see below image).

Hence in a CNO- ion,
Valence electrons given by Carbon (C) atom = 4
Valence electrons given by Nitrogen (N) atom = 5
Valence electrons given by Oxygen (O) atom = 6
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in CNO- ion = 4 + 5 + 6 + 1 = 16

Step #2: Make the rough sketch

CNO- ion (Fulminate ion) has a nitrogen atom at the center and it is surrounded by carbon atom and oxygen atom.

(Remember: This is a CNO- lewis structure, and not OCN- lewis structure.
In OCN- (cyanate ion), Carbon is the center atom. While here in CNO- (fulminate ion), Nitrogen is the center atom.
See the image of OCN- lewis structure for better understanding.)

So now let’s make a rough sketch of CNO- ion (Fulminate ion).

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of CNO molecule, put the two electrons (i.e electron pair) between the carbon atom, nitrogen atom and oxygen atom to represent a chemical bond between them.

These pairs of electrons present between the Carbon (C), Nitrogen (N) and Oxygen (O) atoms form a chemical bond, which bonds these atoms with each other in a CNO molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of CNO, the outer atoms are carbon atom and oxygen atom.

So now, you have to complete the octet on these outer atoms.

Now, you can see in the above image that both the carbon atom as well as oxygen atom form an octet.

Also, all the 16 valence electrons of CNO- ion (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e nitrogen) has an octet or not. 

In simple words, we have to check whether the central nitrogen (N) atom has 8 electrons or not.

As you can see from the above image, the central atom (i.e nitrogen) has only 4 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of nitrogen atom, we have to move the electron pair from the outer atom to form a double bond.

Now the question is, from which atom should we move the electron pair?
From carbon? or
From oxygen? or
Both?

Well, we should move the electron from the atom which is less electronegative. Because the less electronegative atom has more tendency to lose the electrons.

Here, carbon is less electronegative than oxygen. Hence we should move electron pair from carbon.

Still, the octet of nitrogen atom is not fulfilled as it has only 6 electrons.

So again moving the electron pair from carbon atom only, we will get the following structure.

Now you can see from the above image that the central atom (i.e nitrogen), is having 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on Carbon atom (C), Nitrogen atom (N) as well as Oxygen atom (O).

For that, you need to remember the formula of formal charge;

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

• For Carbon:
  Valence electron = 4 (as it is in group 14)
  Nonbonding electrons = 2
  Bonding electrons = 6
• For Nitrogen:
  Valence electron = 5 (as it is in group 15)
  Nonbonding electrons = 0
  Bonding electrons = 8
• For Oxygen:
  Valence electrons = 6 (as it is in group 16)
  Nonbonding electrons = 6
  Bonding electrons = 2

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

Lets keep these charges in the above lewis structure.

As you can see in the above sketch, there are still -1, +1 and -1 charges on the Carbon atom, Nitrogen atom and Oxygen atom respectively. The pair of positive and negative charges gets canceled, which gives the resultant -1 charge on the CNO molecule. And this is the stable lewis structure of CNO- molecule.

Each electron pair (:) in the lewis dot structure of CNO- ion represents the single bond ( | ). So the above lewis dot structure of CNO- ion can also be represented as shown below.

Related lewis structures for your practice:
Lewis Structure of BrO2-
Lewis Structure of N2O4
Lewis Structure of COF2
Lewis Structure of SCl4
Lewis Structure of PBr5 

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