Ionic or Covalent is SO2?

The question of whether sulphur dioxide has an ionic or covalent bond is a particularly common one. Prior to answering the question, it is essential to comprehend key properties of sulphur dioxide. This odourless, poisonous gas indirectly contributes to greenhouse gas.

Despite the fact that sulphur dioxide is not prevalent in the earth’s atmosphere, even minute amounts can have severe health effects. The stench of the odourless gas, which can lead to choking or asphyxia, is unpleasant. Sulfur dioxide is widely employed in the chemical, paper, food, and metal processing industries.

The dilemma that now looms is whether sulphur dioxide is ionic or covalent. Sulfur dioxide is a covalent molecule because two atoms with similar electronegativity attempt to bond in sulphur dioxide. Thus, the tiny variation in electronegativity between the two atoms results in the formation of covalent bonds through the sharing of electron bonds.

Covalently bound compounds are produced when atoms share electrons to complete the structure of an octet.

To comprehend the covalent bond of sulphur dioxide, it is necessary to examine its Lewis Structure, VSEPR theory, and acidic or basic nature.

The Lewis Structure will reveal the resonance structure that leads to the development of the Covalent Bond by Sulfur Dioxide.

The VSEPR Theory assists in establishing the polarity of the Sulfur Dioxide molecule, which influences the SO2 Covalent Bond.

As a result of the Covalent Bond generated by the SO2 molecule, the Sigma and Pi Bonds of SO2 will exert considerable influence.

Sulphur and Oxygen’s Position in the Periodic Table

In the Periodic Table, sulphur is located in group VI A. As the second element of group VI A, sulphur belongs to the third period.

There are three sulphur shells, which are the K, L, and M.

Oxygen also belongs to group VI A, similar to Sulfur. Since oxygen is the first element in the group, it belongs to the second period. It consists of two shells, the K and L. Sulphur Oxygen

The Group VI A VI A

Second First Element Position Within the Group

Period 3rd Period 2nd Period

Number of Shells 3 – K, L, and M 2 – K, L, and M

Total Electron Count: 16,8

Valence Electron Count of 6

Lewis Structure

Diagrammatic representation of the bonds established between the constituents of a molecule, also known as electron dot structure or Lewis dot structure.

Additionally, you must study the essay on the Lewis structure and geometry of SO2.

The schematic representation of the structure reveals that all the molecule’s constituents will have zero formal charges.

The First Resonance Structure

Sulfur has an electronegativity of 2.58 while oxygen’s is 3.44. Since oxygen is relatively more electronegative, it will be positioned on either side.

The nonmetal elements with six valence electrons will therefore form covalent bonds.

With one of the oxygen atoms, sulphur will be able to form a double covalent bond.

Consequently, both atoms will now contain eight electrons.

However, one oxygen atom will be left behind because it requires two electrons.

In this instance, Sulfur will be able to give one lone pair to oxygen, resulting in the development of a coordinate covalent bond.

This simultaneously completes the resonance structure and satisfies the octet rule.

The Second Resonance Structure

As explained previously, Sulfur has three shells and, hence, a d orbit.

If the coordinate Covalent bond is eliminated, a double Covalent bond can be established, allowing for the formation of another resonance structure capable of retaining more than 8 electrons.

In this situation, the molecules will be neutral.

Motives for Resonance

Which of the two resonance structures is more accurate can be questioned.

After testing both structures, we may conclude that the actual structure lies between the two.

For clarity, we can say that Sulfur Dioxide contains two double Covalent bonds and one half-coordinate Covalent bond.

There will be a single intermediate structure because the resonance structures are not continually changing.

Justifications for Intermediate Resonance Structure

The presence of the delocalized pi bond is the underlying explanation for the intermediate resonance structure.

Due to the weak nature of pi bonds, they are able to delocalize, resulting in the formation of a complex intermediate resonance structure.

Theory of VSEPR for Sulfur Dioxide

It is necessary to comprehend the Theory of Valence Shell Electron Pair Repulsion in order to comprehend the geometry of the molecule, as well as its bond angle and polarity, in detail.

According to the idea, electron pairs have a tendency to repel against each other until they reach a location where they are least repellent. Consequently, some molecules are straight while others are curved.

The hybridization process also plays a significant influence. During the process of bond creation, orbits with differing energies deteriorate and lead to the development of a comparable number of identical orbits.

Consider the Sulfur Dioxide molecule (SO2). The atoms of sulphur and oxygen will have hybridised 1s and 2p orbitals.

The SO2 molecule is not linear but twisted (straight). This is the primary cause for the polarity of the SO2 molecule, where the bond angle is 120° and the geometry is trigonal.

Since the SO2 molecule is not linear, charges cannot cancel each other out, resulting in a polar molecule.

Similar to NO2 molecules, NO2 molecules are also bent. Investigate the NO2 geometry.

According to the resonance structure, in which a double Covalent bond will have one sigma and one pi bond, SO2 has two sigma and two pi bonds.

This can be attributed to the two double Covalent bonds that SO2 contains, in which two oxygen atoms each possess one sigma and one pi link.

Acidic Properties of SO2

SO2 is neither alkaline nor basic; it is entirely acidic. Once dissolved in water, it will begin to react with the water molecule, producing sulphurous acid H2SO3.

SO2 + H20 —-> H2SO3

Being a polar molecule, SO2 dissolves easily in water, although sulphurous acid (H2SO3) is a weaker acid than Sulphuric Acid (H2SO4).

SO2 is both an oxidising and reducing agent.

Furthermore, Sulfur Dioxide can operate as both an oxidising agent and a reducing agent, which is an intriguing property.

Sulfur in SO2 has an oxidation state of +4 and can therefore lose two electrons to obtain an oxidation state of +6.

As a result, Sulfur Dioxide may both lose and acquire electrons, making it both an oxidising and a reducing agent.

State dipole of sulphur dioxide

As noted previously, there is a tiny variance in electronegativity within the Sulfur Dioxide molecule.

SO2, as a polar molecule with a difference in electronegativity between sulphur and oxygen atoms, tends to have a dipole state or moment.

Therefore, it is reasonable to assert that SO2 possesses a dipole moment or state with a value of 1.61 Debye.


Sulfur Dioxide (SO2) is a colourless gas with a somewhat pungent odour that is exceedingly dangerous and can induce choking issues. SO2 possesses a covalent link, hence the molecule can be described as a covalent compound.

SO2 contains both a double Covalent bond and a coordinate connection with one oxygen atom. The SO2 consists of hybridised 1s and 2p orbitals. Due to its double Covalent bond, Sulfur Dioxide possesses two sigma bonds and two pi bonds.

SO2 is not linear in nature and has a curved structure. With a bond angle of 120°, SO2 becomes a polar molecule because the charges cannot cancel each other out. When dissolved in water, Sulfur Dioxide generates the weak sulphurous acid H2SO3, and thus SO2 is acidic by nature.

The polar molecule SO2 has a dipole value of 1.61 Debye and functions as both an oxidising and a reducing agent.

Read more: MO Diagram, Lewis Structure, Hybridization, and Molecular Geometry of PCl3

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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