Lewis structure of CNO-

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Lewis structure of CNO-
Lewis structure of CNO–

The Lewis structure of CNO– contains one triple bond and one single bond, with nitrogen in the center, and carbon and oxygen on either side. The carbon atom has one lone pair, the oxygen atom has three lone pairs, and the nitrogen atom does not have any lone pair.

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

Steps

By using the following steps, you can easily draw the Lewis structure of CNO–.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

  • Let’s calculate the total number of valence electrons

We know that… carbon is a group 14 element, nitrogen is a group 15 element, and oxygen is a group 16 element. Hence, carbon has four valence electrons, nitrogen has five valence electrons, and oxygen has six valence electrons.

Now CNO– has one carbon atom, one nitrogen atom, and one oxygen atom.

So the total number of valence electrons = valence electrons of carbon atom + valence electrons of nitrogen atom + valence electrons of oxygen atom

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

Therefore, the total number of valence electrons = 4 + 5 + 6 + 1 = 16

  • Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for carbon, nitrogen, and oxygen as follows:

Electronegativity value of carbon = 2.55
Electronegativity value of nitrogen = 3.04
Electronegativity value of oxygen = 3.44

Obviously, carbon is less electronegative than oxygen and nitrogen. But, we can not assume carbon as the central atom.

Because if we place carbon in the center, then it will become OCN– (cyanate ion).

From nitrogen and oxygen, nitrogen is less electronegative. Hence, assume that nitrogen is the central atom.

So now, put nitrogen in the center and carbon and oxygen on either side. And draw the rough skeleton structure for the Lewis structure of CNO– something like this:

Skeleton structure for Lewis structure of CNO–

Also read: How to draw Lewis structure of N2O4 (5 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since nitrogen is surrounded by carbon and oxygen, use four electrons to show two chemical bonds as follows:

Two chemical bonds shown between atoms

#3 Mark lone pairs

As calculated earlier, we have a total of 16 valence electrons. And in the above structure, we have already used four valence electrons. Hence, twelve valence electrons are remaining.

Two valence electrons represent one lone pair. So twelve valence electrons = six lone pairs.

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

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are carbon and oxygen, so carbon and oxygen will get three lone pairs. And the central atom (nitrogen) will not get any lone pair, because all six lone pairs are used.

So the Lewis structure of CNO– looks something like this:

Lone pairs marked on Lewis structure of CNO–

In the above structure, you can see that the octet is completed on the outside atom. But, the central atom (nitrogen) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of PF6– (4 steps)

#4 Complete octet on central atom

Remember that nitrogen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now nitrogen already has four valence electrons. Hence, nitrogen needs four more valence electrons to complete its octet.

So convert two lone pairs from the carbon atom to make a new bond with the nitrogen atom. And then, the Lewis structure of CNO– looks something like this:

Lone pair of carbon is converted, and octet is completed on atoms

Here, the lone pair of carbon is converted (instead of oxygen). This is because carbon is less electronegative than oxygen, and so it can give more electrons to share them.

In the above structure, you can see that the octet is completed on the central atom (nitrogen), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of XeO4 (5 steps)

#5 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

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

Collect the data from the above structure and then, write it down below as follows:

  • For carbon atom

Valence electrons = 4
Nonbonding electrons = 2
Bonding electrons = 6

Formal charge = 4 – 2 – ½ (6) = -1

  • For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 5 – 0 – ½ (8) = +1

  • For oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of CNO– looks something like this:

Formal charges are calculated, and got the most stable Lewis structure of CNO–

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of CNO–.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now CNO– is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of CNO– looks something like this:

Lewis structure of CNO– showing a negative (-1) charge

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Deep

Rootmemory.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.

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