OCN- 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.

OCN- lewis structure has a Carbon atom (C) at the center which is surrounded by Oxygen atom (O) and Nitrogen atom (N). There is 1 single bond between the Carbon (C) & Oxygen (O) atom and 1 triple bond between the Carbon (C) & Nitrogen (N). There is a -1 formal charge on the Oxygen atom (O).

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

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

Steps of drawing OCN- lewis structure

Step 1: Find the total valence electrons in OCN- ion

In order to find the total valence electrons in an OCN- (cyanate ion) ion, first of all you should know the valence electrons present in oxygen atom, carbon atom as well as nitrogen 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 oxygen, carbon as well as nitrogen using a periodic table.

Total valence electrons in OCN- ion

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. ^[1] 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.

→ Valence electrons given by carbon atom:

Carbon is group 14 element on the periodic table. ^[2] 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. ^[3] 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.

Hence, 

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

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

Now here the given molecule is OCN and it contains oxygen atom (O), carbon atom (C) and nitrogen atom (N).

You can see the electronegativity values of oxygen atom (O), carbon atom (C) and nitrogen atom (N) in the above periodic table.

If we compare the electronegativity values of oxygen atom (O), carbon atom (C) and nitrogen atom (N) then the carbon atom is less electronegative.

So here the carbon atom (C) is the center atom and the oxygen atom (O) and nitrogen atom (N) are the outside atoms.

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

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

This indicates that the oxygen atom (O), carbon atom (C) and nitrogen atom (N) are chemically bonded with each other in a OCN 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 OCN molecule, you can see that the outer atoms are oxygen atom and nitrogen atom.

These outer oxygen and nitrogen 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 OCN- ion.

The OCN- 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 carbon atom (C) is stable or not.

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

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

Now to make this carbon atom stable, you have to shift the electron pair from the outer nitrogen atom so that the carbon 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 nitrogen atom and oxygen atom, then the nitrogen atom is less electronegative.
So you have to shift the electron pair from the nitrogen atom.)

But after shifting one electron pair, the carbon 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 nitrogen atom only. (Because nitrogen is less electronegative than oxygen.)

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

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

And hence the carbon atom is stable.

Now let’s proceed to the final step to check whether the lewis structure of OCN 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 OCN 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 oxygen (O), carbon (C) atom as well as nitrogen (N) atoms present in the OCN 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 OCN molecule in the image given below.

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

For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 8
Nonbonding electrons = 0

For Nitrogen (N) atom:
Valence electrons = 5 (because nitrogen is in group 15)
Bonding electrons = 6
Nonbonding electrons = 2

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

From the above calculations of formal charge, you can see that the oxygen (O) atom has -1 charge, while other atoms have 0 charges.

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

This overall -1 charge on the OCN molecule is represented in the image given below.

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

SiF4 lewis structure	CH3F lewis structure
NH4+ lewis structure	NH2- lewis structure
AlCl3 lewis structure	BeH2 lewis structure