COS Lewis Structure & Characteristics (13 Complete Facts)

Carbonyl sulfide or COS is most abundant gas in stratospheric level which plays symbolic roll in source of life. Let us know about its characteristics in details below.

COS is flammable gas of sulfur compound. It can create sulfur layer which can be oxidized to sulfuric acid in stratospheric level. It affects energy balance due to light scattering in this atmospheric level.

In plants COS is transferred to H2S by catalysis reaction during photosynthesis. Because of this, rate of photosynthesis is measured by analyzing COS in environment. Let us discus some properties like geometry (shape) from hybridization, structure angle, solubility and other facts of COS below. 

How to draw COS lewis structure?

Lewis structure of canonical forms of COS can be drawn through following the steps below.

Step 1: counting total valence electrons of atoms

Total 16 valence electrons are participated in covalent bonds of COS lewis structure. These can be calculated from the group number of the participated atoms in modern periodic table.

Step 2: choosing central atom of COS molecule

Carbon becomes the central atom in the COSlewis structure with greater electro positivity. Electro negativity of oxygen (3.44) and sulfur (2.58) are quite high than carbon (2.55). Hence there is high chance to share electron cloud easily with other atoms for carbon.

Step 3: arrange the electrons and bond formation

The valence electrons are arranged around their parent atoms keeping carbon atom in central. Sigma bonds are drawn in both sides of the carbon joining two electrons from two different atoms. The pi bonds are drawn similarly with straight lines above sigma bonds and octet rule is verified then.

COS lewis structure shape

Shape of covalent molecule can be determined from hybridization of central atom and unshared electron over it. Let us understand shape of COS molecule from VSEPR theory.

COS lewis structure shape is liner similar to its geometry. This is because the central atom carbon is sp hybridized in the molecule. This atom experience similar force from both sides for equal no of lone pairs and double bonds. Hence COS become liner shaped molecule.

cos lewis structure
COS lewis structure shape

COS lewis structure formal charge

COS molecule has different resonating structure as d orbital of sulfur can accommodate delocalized electron. Let us explore formal charge of canonical forms of COS.

COS lewis structure formal charge is zero where central atom carbon is double bonded with both oxygen and sulfur. The calculation for this will be (4- 0- 4/2) = 0 for carbon atom and (6- 4- 4/2) = 0 for both oxygen and sulfur atom.

Another canonical form of COS has also ‘0’ formal charge where oxygen is single bonded and sulfur is triple bonded. This formal charge calculation for oxygen will be (6- 6- 2/2) = (-1) and for sulfur will be (6- 2- 6/2) = (+1). Opposite charges cancel out each other, so molecule has zero charge.

COS lewis structure angle

Structure angle of a covalent molecule is dependent on unshared electrons for its greater repulsion. Let us explain COS lewis structure bond angle with lone pair effect.

COS lewis structure angle (<SCO) is 180 degree between the sulfur, carbon and oxygen atom. Three atoms are attached in liner shape and four lone pairs give similar force from both side. Hence the angle between overlapping orbital can’t be distorted.   

COS lewis structure octet rule

According to octet rule specifically eight electrons can cover last orbit of atom to give stability. Let us explore if stable canonical form of COS obeys the rule.

Atoms of stabilized COS molecule obey octet rule. In this molecule central atom carbon needs 4 more electrons to fulfill the thumb rule. Here oxygen and sulfur atoms share electron cloud to complete the octet of carbon atom. Both of them also satisfy their octet as lack of two electrons.

COS lewis structure lone pairs

Let us know about the lone pairs of COS lewis structure which don’t participate in the bond formation.

COS lewis structure has four lone pairs on side atoms. In stabilized form, each of oxygen and sulfur has two non bonding electron pairs where carbon has no such electron. In another form sulfur has three pairs where oxygen has one lone pair as sulfur can accept delocalized electron in d orbital.

COS valence electrons

Valence electrons are outer orbit electron cloud where nuclear force can’t show strong effect for core electrons. Let us talk about COS structure valence electrons.

COS molecule is formed by sixteen valence electrons while orbital overlapping. Carbon (group 14) atom has four electrons in 2nd orbit and oxygen and sulfur each contains six electrons as group 16 members. These electrons can go to exited state for molecule formation.

cos lewis structure
COS lewis structure valence electrons

COS hybridization

Hybridization is necessary for molecule formation with better overlapping potential with new orbital shape. Let us explain the sp hybridization of COS lewis structure.

Hybridization in COS is sp for the central carbon atom. One 2s orbital electron of carbon transfers to 2p orbital during hybrid orbital formation, so hybridization must be sp3. But here sulfur and oxygen form pi (π) bonds with carbon causing the sp hybridization.

Properties of COS

Let us discuss some properties of the most abundant sulfur compound COS lewis structure.

Property name of COS moleculeData
Molecular weight60.075 g/mol (12.0107+ 15.9994+ 32.065)
Molecular density2.51 g/L
Boiling point(-50.2̊ C)
Melting point(-138.8̊ C)
properties of COS lewis structure

COS solubility

Solubility of COS in any solvent is depended on its polarity at a particular pressure and temperature. Let us find solubility of COS in different solvents.

Solubility of COS is ~0.376 g/ 100 mL water at 0 degree celsius but it decreases to 0.125 g/ 100 mL at 25̊ C. The compound is very much soluble in potassium hydroxide (KOH) and carbon disulfide (CS2). It is also soluble in ethanol, toluene like solvents.

Is COS solid or gas?

Solid or gas is physical state of matter which depends on the force between the constituent atoms at certain temperature. Let us see the state for COS molecule.

COS is colorless gas with unpleasant odor of sulfide. This is because the bonds in molecule are covalent and weak dipole dipole interaction is present between the molecules. Hence the gas has no particular shape with weak intermolecular attraction.

Is COS polar or nonpolar?

COS is polar molecule with dipole moment of 0.65 D. let us explore further about the polarity of COS lewis structure.

COS is a polar molecule as there is electro negativity difference greater than 0.4 in the molecule. Partial charge is developed and dipole moment generates in molecule. With higher electro negativity, the dipole towards oxygen is stronger than dipole of carbon-sulfur, molecule becomes polar. 

Is COS acid or base?

Acidic or basic nature can be explained by capability of producing (H+) or (OH-) ions respectively in water. Let us understand this behavior of COS molecule.

COS is acidic in nature because in reaction with water, (H+) ions generate which form H2S and CO2. Here lone pair of oxygen of water molecule reacts with carbon center of COS. After hydrogen ion transferring, (SH-) forms which producing H2S by accepting another (H+) ion. 

Is COS ionic or covalent?

Molecular bonding is dependent on the process of electron transfer between atoms. Let us explain COS bonds are ionic or covalent.

COS is a covalent compound because sp hybrid orbit electron cloud of carbon atom is shared with sulfur and oxygen atoms to form bonds. But in case of ionic compound, oppositely charged ions are arranged with strong intramolecular electrostatic force.


COS is an important compound in the cycle of Sulfur in land, air and water which emitted from volcanoes, deep sea. By measuring the levels of COS over a period of time, we clearly see the impact of human activities in the ecosystem.

Triyasha Mondal

Hi...I am Triyasha Mondal, pursuing M.Sc in Chemistry. I am an enthusiastic learner. My specialization is in physical chemistry. Let's connect through LinkedIn:

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