CNO- Lewis structure

CNO^– (fulminate) has one carbon atom, one nitrogen atom, and one oxygen atom.

In the CNO^– Lewis structure, there is a triple bond between nitrogen and carbon atom, and a single bond between nitrogen and oxygen atom. The carbon atom has one lone pair, and the oxygen atom has three lone pairs.

Also, there is a negative (-1) charge on the carbon atom and the oxygen atom, and a positive (+1) charge on the nitrogen atom.

Alternative method: Lewis structure of CNO^–

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, nitrogen lies in group 15, and oxygen lies in group 16.

Hence, carbon has four valence electrons, nitrogen has five valence electrons, and oxygen has six valence electrons.

Since CNO^– has one carbon atom, one nitrogen atom, and one oxygen atom, so…

Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of one oxygen atom = 6 × 1 = 6

Now the CNO^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 4 + 5 + 6 + 1 = 16

Learn how to find: Carbon valence electrons, Nitrogen valence electrons, and Oxygen valence electrons

• Second, find the total electron pairs

We have a total of 16 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 16 ÷ 2 = 8

• Third, determine the central atom

We have to place the least electronegative atom at the center.

Since carbon is less electronegative than nitrogen and oxygen, the central atom should be carbon, right?

But if we place carbon in the center and nitrogen and oxygen outside, then it will become OCN^– (cyanate), which is a different compound.

So here, we have to choose the central atom from nitrogen and oxygen.

Since nitrogen is less electronegative than oxygen, assume that the central atom is nitrogen.

Therefore, place nitrogen in the center and carbon and oxygen on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 8 electron pairs. And two bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.

Also remember that all three (carbon, nitrogen, and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are carbon and oxygen.

So for carbon and oxygen, there are three lone pairs, and for nitrogen, there is zero lone pair because all six electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For carbon atom, formal charge = 4 – 6 – ½ (2) = -3

For nitrogen atom, formal charge = 5 – 0 – ½ (4) = +3

For oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

Here, all three atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because all three atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Here we have to convert a lone pair of the carbon atom (instead of the oxygen atom). Because carbon is less electronegative than oxygen. And so, it can give more valence electrons to share them.

Or remember this way, in CNO^– and similar type structures, we have to make sure that the negative charge comes on the most electronegative element. In this case, the most electronegative element is oxygen.

Therefore, convert a lone pair of the carbon atom to make a new C — N bond with the nitrogen atom as follows:

Since there are charges on the atoms, again convert a lone pair of the carbon atom to make a new C — N bond with the nitrogen atom as follows:

Final structure

The final structure of CNO^– comprises a central nitrogen atom connected to a terminal carbon atom and a terminal oxygen atom. Within this layout, the most stable resonance contributor features a triple bond between the carbon and nitrogen atoms and a single bond between the nitrogen and oxygen atoms. The terminal carbon atom retains one lone pair, the central nitrogen atom has no lone pairs, and the oxygen atom fulfills its octet by maintaining three lone pairs. This configuration is highly reactive because it results in significant formal charges—specifically a -1 on the carbon atom, a +1 on the central nitrogen atom, and a -1 on the oxygen atom. Accordingly, this specific electronic distribution serves as the definitive Lewis representation of the fulminate ion.

To complete the representation, draw square brackets around the entire Lewis structure and place a “-” or “-1” sign as a superscript outside the upper right bracket. This notation signifies that the negative charge is a property of the whole ion.

Next: BrO₂^– Lewis structure

External video

• CNO- Lewis Structure: How to Draw the Dot Structure for the CNO- (Cyanate Ion) – YouTube • Wayne Breslyn

External links

• https://lambdageeks.com/cno-lewis-structure/