Lewis structure of OCS

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The Lewis structure of OCS contains two double bonds, with carbon in the center, and oxygen and sulfur on either side. There are two lone pairs on oxygen atom and sulfur atom, and the carbon atom does not have any lone pair.

Steps

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

#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… both oxygen and sulfur are the group 16 elements, and carbon is a group 14 element. Hence, both oxygen and sulfur have six valence electrons, and carbon has four valence electrons.

Now OCS has one oxygen atom, one carbon atom, and one sulfur atom.

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

Therefore, the total number of valence electrons = 6 + 4 + 6 = 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 oxygen, carbon, and sulfur as follows:

Electronegativity value of oxygen = 3.44
Electronegativity value of carbon = 2.55
Electronegativity value of sulfur = 2.58

Obviously, carbon is less electronegative than oxygen and sulfur. Hence, assume that carbon is the central atom.

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

Also read: How to draw Lewis structure of H₃O⁺ (4 steps)

#2 Show chemical bond

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

#3 Mark lone pairs

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

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

Note that both (oxygen and carbon) are the period 2 elements, so they can not keep more than 8 electrons in their last shell. And sulfur is a period 3 element, so it can keep more than 8 electrons in its 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 oxygen and sulfur, so oxygen and sulfur will get three lone pairs. And the central atom (carbon) will not get any lone pair, because all six lone pairs are used.

So the Lewis structure of OCS looks something like this:

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (carbon) 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 AsH₃ (4 steps)

#4 Complete octet on central atom

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

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

So convert one lone pair from oxygen atom and sulfur atom to make a new bond with the carbon atom. And then, the Lewis structure of OCS looks something like this:

In the above structure, you can see that the octet is completed on the central atom (carbon), 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 Br₃^– (4 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 oxygen atom

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

Formal charge = 6 – 4 – ½ (4) = 0

• For carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• For sulfur atom

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

Formal charge = 6 – 4 – ½ (4) = 0

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

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of OCS.

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

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Related

• Lewis structure of H₃O⁺
• Lewis structure of AsH₃
• Lewis structure of Br₃^–
• Lewis structure of SeF₆
• Lewis structure of Br₂

External links

• Drawing the Lewis Structures for OCS – The Geoexchange
• OCS Lewis Structure in 6 Steps (With Images) – Pediabay
• What is the Lewis structure of OCS? – Socratic
• What is the Lewis structure for OCS? – Homework.Study.com
• OCS lewis structure, molecular geometry, bond angle, hybridization – Topblogtenz
• OCS Lewis Structure, Geometry, Hybridization, and Polarity – Techiescientist
• OCS, has three possible Lewis structures – Chegg
• Write Lewis structure that obeys the octet rule for OCS and assign formal charges to each atom – Brainly
• Draw the Lewis structure with lowest formal charges, and determine the charge of each atom in OCS – Quizlet
• DRAW the THREE possible Lewis structures of OCS (C is the central atom) – Numerade
• OCS (Carbonyl Sulfide) Oxidation Number – ChemicalAid