OCS 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.

OCS lewis structure has a Carbon atom (C) at the center which is surrounded by one Oxygen atom (O) and one Sulfur atom (S). There are 2 double bonds between the Carbon atom (C) & Oxygen atom (O) as well as between the Carbon atom (C) & Sulfur atom (S). There are 2 lone pairs on the Oxygen atom (O) and Sulfur atom (S).

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

So let’s move to the steps of drawing the lewis structure of OCS.

Steps of drawing OCS lewis structure

Step 1: Find the total valence electrons in OCS molecule

In order to find the total valence electrons in OCS molecule, first of all you should know the valence electrons present in oxygen atom, carbon atom as well as sulfur 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 sulfur using a periodic table.

Total valence electrons in OCS molecule

→ 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 sulfur atom:

Sulfur is a group 16 element on the periodic table. ^[3] Hence the valence electrons present in sulfur is 6.

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

Hence, 

Total valence electrons in OCS molecule = valence electrons given by 1 oxygen atom + valence electrons given by 1 carbon atom + valence electrons given by 1 sulfur atom = 6 + 4 + 6 = 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 OCS and it contains oxygen atom (O), carbon atom (C) and sulfur atom (S).

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

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

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

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

Now in the OCS molecule, you have to put the electron pairs between the oxygen, carbon and sulfur atoms.

This indicates that these atoms are chemically bonded with each other in a OCS 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 OCS molecule, you can see that the outer atoms are carbon atom and sulfur atom.

These outer 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 OCS molecule.

The OCS molecule has a total 16 valence electrons and all these valence electrons are used in the above sketch of OCS.

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 oxygen atom so that the carbon atom can have 8 electrons (i.e octet).

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 sulfur atom.

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 OCS 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 OCS.

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) atom, carbon (C) atom as well as sulfur (S) atom present in the OCS 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 OCS molecule in the image given below.

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

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

For Sulfur (S) atom:
Valence electrons = 6 (because sulfur is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
O	=	6	–	4/2	–	4	=	0
C	=	4	–	8/2	–	0	=	0
S	=	6	–	4/2	–	4	=	0

From the above calculations of formal charge, you can see that the oxygen (O), carbon (C) atom as well as sulfur (S) atom has a “zero” formal charge.

This indicates that the above lewis structure of OCS is stable and there is no further change in the above structure of OCS.

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

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:

H3O+ Lewis Structure	CH3NO2 Lewis Structure
AsH3 Lewis Structure	SeF6 Lewis Structure
AsF3 Lewis Structure	KrF2 Lewis Structure