SO2 ionic or covalent: Everything about SO2’s bonding

Are you curious to know about the bonding of SO2? Is it ionic or covalent? Is it polar or non polar molecule? Whether it’s acidic or basic? Or do you want to know details about the bonding of SO2? In this article we are going to cover all the topics related to the bonding of SO2. From basics to details of the bonding and structure of SO2.

We are going to discuss about Lewis structure of SO2, resonance structures, it’s geometry and hybridization according to VSPER theory and some of it’s properties related to it’s bonding like dipole moment and acidic or basic nature of SO2.

Note: If you are not looking for detail and searching for direct answers you can check the “Conclusion”.

Condition of Sulphur in ground state:

Sulphur belongs to VI A group of periodic table. It is the second element of it’s group and belongs to 3rd period (the group starts from 2nd period, as you can see below). So according to it’s position in periodic table, sulphur has 3 shells K, L and M and it has 16 electrons. The valence shell contains 6 electrons. The electronic configuration of sulphur will be 1s², 2s², 2p⁶, 3s², 3p⁴.

Condition of Oxygen in ground state:

Like sulphur oxygen also belongs to VI A group of periodic table. It is the first element of its group so it’s in 2nd period (as the group starts from 2nd period). Sulphur has 2 shells K and L. It has 8 electrons in total and 6 valence electrons. It’s electronic configuration is 1s², 2s², 2p⁴.

Fun fact: During volcanic eruption, SO2 gas is released in large quantities.

Lewis structure of SO2:

What is Lewis structure?

Before getting into the Lewis structure of SO2. Let’s see what Lewis structure actually is. Lewis structure which is also known as electron dot structure or Lewis dot structure is a diagrammatic representation of the bonds formed between the elements of a molecule. These structures are drawn in a manner to make the formal charges 0 for all the elements of the molecule.

If the formal charges are not zero we try to make them zero by changing the bonds and by moving electrons. In these cases we get more than 1 structure for a single molecule. These structures are called resonance structures.

Rules for drawing Lewis structure:

For drawing the lewis structure we have to follow some steps.

1.Draw the less electronegative element in center. More electronegative elements will be on sides.

2.Draw the valence electrons (electrons of outermost shell) of all elements.

3.Start filling the valence orbits to get 8 electrons by drawing bonds.

4.Check the formal charges or oxidation number.

This is the overview of the method for drawing the lewis structure.

1st resonance structure:

Oxygen is more electronegative than sulphur so we have placed it on sides. Sulphur has electronegativity of 2.58 while oxygen has 3.44. Now we have to start making bonds. As both the elements are non metals and have 6 valence electrons so they will form covalent bonds.

1.Sulphur will make double covalent bond with 1 oxygen atom. In this way both the atoms will get 8 electrons.

2.But we have another oxygen left and it needs 2 electrons so sulphur can donate it’s 1 lone pair to oxygen atom and forms a coordinate covalent bond.

3.Our structure is complete and satisfy octet rule as well. Let’s look at the formal charges of these atoms.

Formal charge check:

But how will you find the formal charges? There is a formula for that, “valence electrons – (non bonded electrons + bonds formed)”.

For sulphur:

Sulphur had 6 valence electrons and now sulphur has 2 non bonded electrons and 3 bonds with 2 oxygen atoms. Let’s put these values in our formula
6 – (2+3) = +1

For Double bonded oxygen:

Oxygen also had 6 valence electrons and now it has 4 non bonded electrons and 2 bonds with sulphur so,
6 – (4+2) = 0

For 2nd oxygen:

It also had 6 valence electrons. After bonding it has 6 non bonded electrons and 1 bond with sulphur so,
6 – (6+1) = -1

2nd resonance structure:

The second structure is same as the first one we just flip the bonds of oxygen atoms.

Formal charge check:

For Sulphur:

The situation is same as before for the sulphur atom.
6 – (2+3) = +1

For Double bonded oxygen:

It had 6 valence electrons and now it has 4 no bonded electrons. 2 bonds are formed with sulphur.
6 – (4+2) = 0

For 2nd oxygen atom:

It has 6 non bonded electrons and 1 bond with sulphur so,
6 – (6+1) = -1

As we can see by changing the position of bonds the charges have changed their position as well. But our molecule is still not neutral.

3rd resonance structure:

We all know that sulphur has a d orbital (since it has 3 shells). It has the capacity to hold more electrons than 8. So if we remove the coordinate covalent bond and make a double covalent bond our molecule will become neutral.

Formal charge check:

For sulphur:

Now it has 2 non bonded electrons and 4 bonds so,
6 – (2+4) = 0

For oxygen atoms:

Both oxygen atoms have 4 non bonded electrons and 2 bonds with sulphur so,
6 – (4+2) = 0

You can check the following video regarding lewis structure of SO2.

Cause of the resonance:

You might be a little confused that which structure is actually correct? Practically we have found that the real structure is some what between these structures. For understanding we can say that it has 2 double covalent and half coordinate covalent bond.

The structures are not continuously flipping but there is only one intermediate structure. So the resonance structures are represented in the following way with the help of double sided arrow.

Reason for intermediate structure:

But why is it an intermediate structure? It is because of delocalized pi bond. The pi bonds are weak so they can delocalize themselves and we see an intermediate strange structure that is difficult to understand. But it’s not difficult for the nature to create it.

Geometry of SO2 according to VSEPR theory:

Valence shell electron pair repulsion (VSEPR) theory gives the explanation about the geometry of a molecule. It’s bond angle and about it’s polarity.

According to this theory the electron pairs repel each other to a position of least repulsion. Due to this reason some molecules are straight and some are bent.

There is another thing called hybridization. It happens during bond formation. The orbitals have different energies so they degrade themselves and make same number of identical orbitals (same shape and energy).

Now let’s look to the molecule of SO2. In SO2 sulphur and oxygen atoms, all are sp2 hybridized (1 s and 2 p orbitals are hybridized). So the molecule of SO2 is not linear it’s bent. The bond angle is 120° and it has trigonal geometry. This geometry is the reason for SO2’s polarity. Since this molecule is not linear so the charges don’t cancel each other’s effect and SO2 becomes a polar molecule.

Pi and Sigma bonds of SO2:

You may be wondering how many pi and sigma bonds does SO2 have? Well SO2 has 2 pi and 2 sigma bonds. This is according to the third resonance structure. In one double covalent bond there is always 1 sigma and 1 pi bond present. SO2 has 2 double covalent bonds. 1 with each oxygen atom so it has 2 pi and 2 sigma bonds.

Fun fact: Sulphur dioxide causes acid rain. It reacts with water vapors of air and form H2SO3 acid which comes down with rain. That’s why SO2 cause pollution.

Is SO2 acidic or basic?

SO2 is acidic. If you dissolve SO2 in water it will react with water molecules to give sulphurous acid (H2SO3). If you are thinking that will SO2 dissolve in water? So, yeah definitely SO2 is a polar molecule so it can easily dissolve in water. Unlike sulphuric acid H2SO3 is a weak acid.

SO2 + H2O → H2SO3

Chemistry of SO2

Is SO2 reducing agent or oxidizing agent?

Sulphur dioxide can be categorized into both types. Yes, SO2 can act as a reducing agent as well as a oxidizing agent. The reason behind this behavior is that sulphur has a +4 oxidation state in SO2 molecule. So it can either oxidize itself to +6 oxidation state (act as a reducing agent).


In the following reactions sulphur has gained +6 oxidation state.

2SO2 + O2 →2SO3

SO2 + Cl2 → SO2Cl2

Or it can reduce itself to -2 oxidation state (act as an oxidizing agent).


SO2 + 3H2 → H2S + 2H2O
In this reaction sulphur has -2 oxidation state in H2S

Fun fact: SO2 has temporary bleaching effect. It is because it acts as reducing agent and remove oxygen from the colored compounds. The removal of oxygen makes the substance colorless. However, soon atmospheric oxygen takes it’s place and color reappears.

Dipole moment of SO2:

You might be wondering about the dipole moment of SO2. As it is mentioned above that in SO2 there is a difference of electronegativity between sulphur and oxygen atoms and it is also a polar molecule so it should have a dipole moment. The answer to this question is yes, sulphur dioxide has a dipole moment and it has the value of 1.61 Debye.


1.SO2 or sulphur dioxide is colorless gas with a pungent smell.

2.It is a covalently bonded molecule. SO2 contains double covalent bond with one oxygen atom and a coordinate covalent bond with the other one.

3.Sulphur dioxide has sp2 hybridization in both sulphur and oxygen atoms.

4.It contains 2 sigma and 2 pi bonds

5.SO2 is not linear it has bent structure and has trigonal geometry. It has a bond angle of 120°. Due to this structure of SO2 it is a polar molecule because the charges can’t cancel the effect of each other.

6.SO2 is acidic in nature. The reason behind this is that SO2 reacts with water to form H2SO3 or sulphurous acid which is a weak acid.

7.This molecule act as oxidizing as well as reducing agent because it has +4 oxidation state. So it can change its oxidation state to a higher as well as to a lower level.

8.Since the molecule is polar so it has a dipole moment of 1.61 Debye.

So now you know all about SO2. Whether it is ionic or covalent, polar or non polar, acidic or basic. You now know the answers and the reasons for all that as well.

Read also:
N2O Lewis Structure
H2O Lewis Structure
Write the structure of 2 methyl cyclohexane?
Types Of Chemical Reactions

Sulfur dioxide molecule contains one sulfur atom or two oxygen atoms. We would construct the lewis structure of the SO2 molecule by following VSEPR theory rules or considering stability of the intermediate structures. After obtaining the lewis structure of the SO2, we may determine the hybridization of the atoms.

Sulfur dioxide SO2

Sulfur dioxide is the the colourless inorganic gas or also the toxic gas. this gives the weak acid solution if dissolves in the water. This gas is the produced due to the combustion of the petroleum fuel in the automobiles or industrial factories.

Lewis structure of the SO2

There are the two double bonds between sulfur atom or oxygen atoms in the SO molecule. Also, the lone pair exists on the sulfur atom or each oxygen atom has two lone pairs in the SO2 lewis structure.

Hybridization of the SO2

All atoms have sp2 hybridization. Each oxygen atom has one sigma bond or two lone pairs. Therefore, oxygen atoms’ hybridization should be sp2. for the sulfur atom, there are the two sigma bonds or one lone pair to the make hybridization sp2. Simple method to the determine the hybridization of the atoms in the covalent compounds.

Apply VSEPR theory - Steps of the drawing lewis structure of the SO2

Following steps are the used to the draw the lewis structure of the SO2. Each step is the explained in the detail in the next sections. If you are the beginner to the lewis structure drawing, follow these sections slowly or properly to the understand this completely. Look the figures to the understand each step.

  1. Find total number of the electrons of the the valance shells of the sulfur or oxygen atoms

  2. Total electrons pairs

  3. Center atom selection

  4. Put lone pairs on the atoms

  5. Check the stability or minimize charges on the atoms by converting lone pairs to the bonds until most stable structure is the obtained.

Total number of the electrons of the valance shells of the ethene

Both sulfur or oxygen belongs to the group VIA elements series. Therefore, they have six electrons in the their valence shell. to the find number of the valence electron, these valence electrons of the each element should be multiplied with the their respective number of the atoms in the molecule. Below, this step are the done.

• Total valence electrons given by two oxygen atoms = 6 * 2 = 12

• Total valence electrons given by sulfur atom = 6 * 1 = 6

There are the no charges in the SO2 molecule. Therefore, no addition or reduction of the valence electrons due to the charges.

• Total valence electrons = 12 + 6 = 18

Total valence electrons pairs

Total valance electrons pairs = σ bonds + π bonds + lone pairs at the valence shells. Total electron pairs are the determined by dividing the number total valence electrons by two. For, SO2 molecule, Total number of the pairs of the electrons are the 9.

Center atom or sketch of the ethene molecule

There are the few requirements to the be the center atom. Having the high valence is the the main requirement to the be the center atom. for the SO2 molecule, sulfur has the highest valence than or oxygen.

Mark lone pairs on the atoms

After drawing the sketch, we should start to the mark lone pairs on the atoms. In the drawn sketch, there are the two bonds. between atoms.

• There are the already two S-O bonds in the the above sketch. Now, there are the just seven (9-2 = 7) valence electrons pairs are the remaining to the draw (as mark lone pairs) the rest of the structure.

• First, mark remaining valence electrons pair as the lone pairs on the oxygen atoms (outside atoms). Six valence electron pairs are the marked on the two oxygen atoms. Now, there are the still one valence electron pair is the remaining. this is the marked on the sulfur atom as the lone pair.

• Now, all valence electron pairs are the marked as bonds or lone pairs in the sketch.

Charges on the atoms

Charges on the atoms are the important to the find the most stable structure. Therefore, we need to the find the most stable structure to the obtain lewis structure. Therefore, we should try to the find charges if there are.

After, marking electron pairs on the atoms, we should mark charges of the each atom. Each oxygen atoms would take the -1 charge or sulfur atom take the +2 charge. Because SO2 is the neutral molecule, overall charge of the molecule should be zero. The overall charge of the molecule is, (-1) * 2 + (+2) = 0.

Stability of the structure or minimize charges on the atoms by converting lone pairs to the bonds

When there are the positive or negative charges on the lot of the atoms or higher charges (like +2, +3, -2, -3) on the atoms in the an ion or molecule, this structure is the not stable. Therefore, We should try to the reduce charges on the atoms if this is the possible. in the thee above structure, there are the charges on the oxygen atoms or sulfur atom. Now, we are they going to the reduce charges on the these atoms as below.

• Now, we should try to the minimize charges by converting the lone pair or pairs to the bond. So convert the lone pair on the oxygen atom to the make the new S-O bond with the sulfur atom as the following figure.

• Now there is the double bond between one oxygen atom or sulfur atom. You may see, charges are the reduced now in the new structure.

• Because, there are the still charges on the atoms, we may try to the convert the lone pair to the bond. So, convert the lone pair on the other oxygen atom to the make the bond with the sulfur atom. with the that, there are the no charges on the sulfur or oxygen atoms.

• Therfore, this structure should be the lewis structure of the SO2

How many lone pairs sulfur has in the SO2

There is the just one lone pair on the valence shell of the sulfur atom.

SO2 lewis structure lone pairs

There are the lone pairs on the all atoms in the SO2. Sulfur atom has one lone pair or each oxygen atom has two lone pairs. Therefore, there are the total of the five lone pairs on the last shells of the each atom in the SO2.

What are the other similar lewis structures of the SO2?

If we consider the shape of the SO2, water, nitrogen dioxide, hydrogen sulfide, ozone have similar shape, bent. Also, if number of the sigma bonds are the is the considered, water, nitrogen dioxide, hydrogen sulfide, sulfur dioxide all have two sigma bonds. Both SO2 or ozone has one lone pair on the center atom.

Are there similarities in the SO2 or NO2 lewis structures?

Actually, this question is the weird one. Rather than discussing similarities, it’s good to the discuss their differences. in the NO2 lewis structure, there is the an unpaired electron on the nitrogen atom.

What are the similarities or differences in the SO2 or SO3 lewis structures?

• Around sulfur atom, summation of the lone pair or sigma bonds is the three in the both SO2 or SO3. Therefore, sulfur atom has sp2 hybridization.

• But, shapes around sulfur atom in the SO2 or SO3 are the different. in the SO2, shape around sulfur atom is the bent. But in the SO3, shape is the trigonal planar.