Ever wondered what causes the smell when matchsticks are burnt? Well, the answer is SO2!
SO2 is a very beneficial gas. Along with its main use, i.e sulfuric acid formation, SO2 has multiple functions in this chemical industry.
But before going through them, pause a little and give a read to this article. Because in the end, you will have deep knowledge about all the basics of SO2 you need to know, before moving on with the reactions.
So let’s begin!!
Sulfur dioxide is spelled as Sulphur dioxide in Commonwealth English. This is a pungent-smelling, colorless gas.
Talking about its properties, SO2 has a molar mass of 64.066 g/mol. The melting point and boiling points are -72℃, and -10℃ respectively.
Now let’s move on to the fundamental concepts like lewis structure, molecular geometry, MO Diagram, and hybridization of SO2.
SO2 Lewis Structure
Before directly jumping into the lewis structure of SO2, let’s have a quick discussion regarding the importance of lewis structure and the steps to draw it.
Lewis structure is the distribution of the electrons around the atoms of a compound.
This structure helps us to know about the kind of bonds and the number of bonds that form the compound.
Now let’s walk through the method of drawing lewis structure:
Step 1 – Figuring out the total number of valence electrons in the molecule is the first and most important step. While doing so, do take care of the +, – signs. A ‘+’ sign means losing electrons and ‘-‘ means gaining.
Steps 2 – Next thing is figuring out the central atom. The atom with the highest number of bonding sites is the central atom.
Step 3 – The third step is creating a skeleton structure with single bonds only.
Step 4 – Next, our work is completing the octet of the atoms with the remaining electrons, after the formation of the single bonds. Always begin with the electronegative atoms then move to the electropositive ones.
Step 5 – Giving double or triple bonds is necessary if it is needed for fulfilling the octet rule for all atoms.
Step 6 – At last, it’s important to check if all the atoms are having their lowest possible formal charge. Formal charge calculation can be done using:-
Now let’s see the lewis structure of SO2.
In SO2, the sulfur’s valence electron = 6
And the valence electrons of oxygen = 6
There are 2 oxygen atoms in the compound, thus = 6*2 = 12
So, total valence electrons = 18
After drawing the skeletal structure, we can see that none of the atoms can fulfill their octet with single bonds. So there is a need for a double bond. Thus the number of electrons used in double bonds = 8
Subtracting that from the total valence electrons we get 10 electrons remaining. We need to place these remaining electrons around the atoms as per the requirement.
This will finally complete the octet of the atoms. Oxygen has 2 lone pairs and sulfur has 1 lone pair.
At last, don’t forget to check the formal charge of all the atoms!
The next topic we need to know is the hybridization of SO2.
The hybridization of SO2 is Sp2.
Now hybridization of SO2 can be understood in two ways, one is the theory and the 2nd is directly applying the formula. I would suggest learning the theory first and then you can surely go for the formal.
A quick tip for you, when 1 s orbital unites with 2 p orbitals it results in Sp2 hybridization having 3 equivalent orbitals.
Likewise, in case of SO2, the ground state electronic configuration is 1s2 2s2 2p6 3s2 3p4. When in an excited state, one electron from 3px, moves to 3d orbital. Thus we have 3p3.
Now, the 3s2 and 3p3 combine to form Sp2 hybridization with 3 equivalent orbitals, containing 2 paired electrons and 2 unpaired.
For forming 2 sigma bonds with oxygen atoms, sulfur needs the 2 unpaired electrons from the Sp2 hybridized orbitals. And the remaining 2 paired orbitals form the lone pair of sulfur.
Wondering about the other 2 electrons of 3p which were not involved in hybridization?
Well, those two (i.e one of the 3p orbital and another electron in 3d) formed the 𝞹 bonds between sulfur and oxygen. There’s an image attached below for better understanding.
Now coming to the formula part.
The formula for finding hybridization of any compound is;
H = ½ [ V+M-C+A]
- H depicts Hybridization
- V is the no. of valence electrons
- M is the number of monovalent atom present
- C depicts the cationic charge
- A depicts the anionic charge
Here, if H is 2, it’s Sp hybridization
When, H = 3, it’s Sp2 hybridization.
When, H = 4, it’s Sp3 hybridization
By the same token H = 5, its Sp4 hybridization
And lastly, when, H is 6, it will be Sp3d2 hybridization.
For SO2, the number of valence electrons of the S atom = 6 and the number of monovalent atoms = 0, because oxygen is a divalent atom.
Here cationic and anionic charges will be 0 as it’s a neutral compound.
Thus, H = ½ [6+0-0+0]
H = ½ * 6
H = 3 = Sp2 hybridization.
I hope the hybridization of SO2 is clear from both the explained concepts.
SO2 Molecular geometry
The molecular geometry of SO2 is bent, with a bond angle of 120°.
We can easily find out the molecular geometry of any compound using the given chart.
Here, A = central atom, X = surrounding atoms and E = the lone pairs. SO2 is an AX2E type molecule, with 2 surrounding atoms i.e oxygen, and 1 lone pair of sulfur.
But the electron geometry of SO2 is trigonal planar. You must be wondering about this new term, right? Let me explain.
So, electron geometry is different from molecular geometry because it considers all the electron pairs (including lone pairs) while determining the shape. Whereas molecular geometry considers only the atoms.
In absence of a lone pair, both the geometries are the same for any compound.
Below is the 3D view of the geometry of the SO2 molecule.
Now let’s learn the last topic of this article, the molecular orbital diagram of SO2.
SO2 Molecular Orbital Diagram
The molecular orbital diagram of SO2 is attached below:
A molecular orbital diagram gives us an idea about how the atomic orbitals of two different atoms can fuse and give rise to a new orbital.
This further helps us to find out the bond order, bond length, and bond strength of any compound.
In this MO we can see that the AO of sulfur, which is on the left-hand side combines with the AO of oxygen on the right-hand side.
We can see 18 electrons are filled in the orbitals with the proper rule.
There are certain non-bonding orbitals present there as well. Also, the antibonding orbitals are empty in the case of SO2.
This sums up the explanation about the molecular orbital diagram of SO2.
The SO2 molecule is classified as a polar molecule because of the imbalance of charge across the atoms in the molecule.
The sulfur being more electronegative than oxygen pulls the charge to its side and gains a partial negative charge. therefore the polarization exists.
You can also refer to the article written on the polarity of SO2.
Now, let us also move to its preparatory methods
SO2 can be produced in several methods. I am breaking down each method to make it easy to digest!
Method 1 – The main production of SO2 is during the manufacture of sulfuric acid using the contact process. Among all other ways to manufacture SO2, this method is widely used in industries.
( Because Chemistry has a lot to do with history, here’s a historical fact for you! In 1979, the United States used 23.6 million tonnes of SO2 for manufacturing sulfuric acid !)
Method 2 – SO2 can be produced by burning sulfur or materials containing sulfur.
S + O2 ——-> SO2
2 H2S + 3O2 ——–> 2H2O + 2SO2
Method 3 – SO2 production can also be done by the roasting of pyrite, sphalerite, and cinnabar ( sulfide ores).
Method 4 – In the formation of calcium silicate cement, SO2 is produced as a byproduct.
2 CaSO4 + 2SiO2 + C ———> 2CaSiO3 + 2SO2 + CO2
Method 5 – In the laboratory, the reaction between hot concentrated sulfuric acid and copper turnings leads to SO2 formation.
Cu + 2H2SO4 ——–> CuSO4 + SO2 + 2H2O
Method 6 – Natural calamities like volcanic eruptions can produce a large amount of SO2.
Now let’s move on to the lewis structure of SO2!
This article explains pretty much everything you need to know about SO2.
Before studying the reactions and equations involving SO2, go through this article to clear all your concepts regarding lewis’s structure, geometry, hybridization, and MO diagram of SO2.
If you have any doubt feel free to contact me anytime. Have a happy reading!