SO2 ionic or covalent: Everything about SO2’s bonding SO2 is a covalent compound. Covalently bonded compounds are formed when atoms share electrons to complete an octet. Here, when two atoms with similar electronegativity are bonded, a slight difference in their electronegativity leads to the sharing of bound electrons.
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
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).
Example:
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).
Example:
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.
Conclusion:
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