Structure, Geometry, Hybridization, and Polarity in OCS Lewis

Carbonyl Sulfide, sometimes known as COS, is a well-known and abundant stratospheric gas with the chemical formula OCS. It has a tremendous impact on life on land, air, and water as part of the sulphur cycle. Sulfur, on the other hand, is a poisonous element for humans and animals, and acute exposure can result in death.

Carbonyl sulphide is a prevalent gas on Venus, in case you didn’t know. Scientists assume there is life on Venus as a result of this, yet there is no proof.

Because carbonyl sulphide is the primary source of sulphur on Earth, it is critical to comprehend its molecular behaviour.

The Lewis structure is a diagram that depicts electrons collaborating in bond creation to create new compounds with novel chemical characteristics.

As a result, it is the best spot to start studying carbonyl sulfide’s behavioural features.

Carbonyl Sulfide Lewis Structure (COS)

The Lewis structure is created by drawing valence electrons in pairs around the symbol of an element in the middle.

The valence electrons are found in the atom’s outermost shell and play a role in bond formation.

This is explained by the structure of an atom, in which the nucleus is in the core and electrons orbit around it in their orbits.

The nucleus provides an attractive force on electrons, allowing them to display their intrinsic features without hopping to other orbits.

According to this logic, the nucleus’s force of attraction will be weaker the farther the orbit is from the nucleus. As a result, electrons in the outermost shell are unaffected by the nucleus’s pull and can easily bond with another element nearby.

Eight valence electrons are the maximum number that an atom can have.

To begin studying the Lewis structure of carbonyl sulphide, we must first study the same for all of the involved elements.

The atomic number of carbon is six, and it possesses four valence electrons.

The atomic number of oxygen is eight, meaning it possesses six valence electrons.

The atomic number of sulphur is 16 and it possesses 6 valence electrons.

How to Draw the Lewis Structure of Carbonyl Sulfide in Simple Steps

Step 1: Calculate the valence electrons for each of the atoms involved: Carbon has a value of four, while oxygen and sulphur have a value of six.

Step 2: To sketch the Lewis structure of carbonyl sulphide, determine the total amount of valence electrons available: It takes 16 OCS molecules to make one OCS molecule.

Step 3: Calculate how many additional valence electrons are required to stabilise one carbonyl sulphide molecule: The total number of valence electrons required is 24, hence the answer is 8.

Step 4: Determine the type of bond that is forming between the atoms involved: As oxygen and sulphur connect with carbon for only two valence electrons apiece, a double bond will develop.

Step 5: Look for the main atom: Carbon will be chosen since it has the lowest electronegativity value of the three atoms involved.

Step 6: Draw the Lewis structure of carbonyl sulphide using all of the previously mentioned points:

Why do carbonyl sulphide molecules create double bonds?

Both oxygen and sulphur atoms require two valence electrons to complete their octet, as shown in the structure. Because carbonyl sulphide is a covalent molecule, it is impossible to donate valence electrons.

As a result, all of the participating atoms share valence electrons in order to reach a stable state.

The only double bond with which the molecule has achieved a stable state is the single bond, which has an odd number of valence electrons.

Why is it necessary for a molecule’s core atom to have the lowest electronegativity?

The reason for this is that the lower the electronegativity value, the greater the tendency to share electrons.

The core atom must have low electronegativity in order to share the majority of its valence electrons.

Otherwise, the core atom’s valence electrons will not be shared, and no new molecule will be formed.

Carbonyl Sulfide Molecular Geometry (OCS)

Because all three contributing atoms are placed at 180° from one another in the Lewis structure, it is obvious that the molecular geometry of carbonyl sulphide is linear.

The Valence Shell Electron Pair Repulsion (VSEPR) Theory can also be used to study the molecular geometry of this molecule in greater depth.

The bond length between oxygen and carbon is 115.78 pm, while the bond length between sulphur and carbon is 156.01 pm.

The carbonyl sulphide molecule has a symmetrical shape due to the double bonds between oxygen and sulphur, as well as the equal amount of lone pairs of electrons on both sulphur and oxygen atoms.

The molecular geometry can be further investigated using the structural model shown below:

It’s possible that the fact that carbonyl sulphide has a linear chemical structure while possessing a lone pair of electrons confuses you.

Because there are an equal amount of lone pairs of valence electrons on oxygen and sulphur, the total effect cancels out, making the structure symmetric.

As a result, the carbonyl sulphide begins to behave like a linear molecule. The structure of carbonyl sulphide would be trigonal planar if there were uneven lone pairs of valence electrons.

Carbonyl Sulfide Hybridization (OCS)

Carbonyl sulphide has sp hybridization since it is a linear molecule. Because the carbonyl group is sp2 hybridised, it may appear unusual to some.

It’s vital to note that the carbonyl group generally takes on a tetrahedral structure with a bond angle of 120°, but this isn’t the case with carbonyl sulphide, which has linear molecular geometry.

Sp hybridization happens in carbonyl sulphide when three participating atoms are organised in a linear pattern, causing one s and one p orbital of the same shell within an atom to mix, resulting in two new orbitals of equal energy.

A double bond is made up of one sigma bond and one pi bond, making it a stronger link than others because both sigma and pi bonds have the same effect on the bond.

Despite the fact that sigma bonds are more stronger than pi, the molecule has different chemical properties as a result of them.

Hybridization is a mathematical process for discovering the reason for the development of bonds between the atoms in a molecule.

It investigates how distinct atomic orbitals interact with an atom, resulting in the generation of new atomic orbitals with similar energies.

It takes it a step further by presenting a molecular orbital diagram, which allows participants’ atomic orbitals to be explored in greater depth.

Carbonyl Sulfide Polarity (OCS)

The separation of electrical charges that creates cationic and anionic ends within an atom is known as polarity. This characteristic determines whether an atom accepts or shares its valence electrons.

To calculate the polarity of any element, all of the participating atoms’ electronegativity values must first be determined.

Values of electronegativity for:

2.55 grammes of carbon

2.58 Sulfur

3.44 ppm of oxygen

To be polar in nature, the difference between the core atom and the other participating atoms must be bigger than 0.4.

If the difference between the two is less than 0.4, the bond becomes nonpolar.

Let’s do the math for carbonyl sulphide now (COS)

Carbon – Oxygen = 0.89

The C=O bond becomes polar when the electronegativity difference exceeds 0.4, making the entire carbonyl sulphide molecule polar in nature.

Carbonyl sulfide’s polar character can also be explained by the fact that its net dipole moment is not zero.

Because of the substantial disparity in electronegativity levels, the carbon-sulfur and carbon-oxygen bonds do not neutralise each other’s influence. A dipole cloud forms on the carbonyl sulphide molecule as a result, making it polar.


Carbonyl sulphide (OCS or COS) is a linear molecule that does not show the real nature of the carbonyl group. It prefers to be simple and exhibit chemical features with no exceptions because it is the simplest of all carbonyl groups.

Carbonyl sulphide is made up of three components that are connected in a linear pattern by a double bond with the centre atom. Because the overall structure is symmetrical, the parts on both ends exert an equal amount of repulsion.

Carbonyl sulphide is polar despite the fact that linear molecules tend to be nonpolar due to a bigger disparity in the electronegativity values of the involved atoms, which generates a dipole cloud on the molecule. Carbonyl sulphide is sp hybridised and has equal s and p properties due to its symmetrical linear structure.

Read more: Is HBr a Base or an Acid?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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