Carbon dioxide is a colorless gas that is well known to many of us!
From the time we were in school, we knew that we inhale oxygen and exhale CO2. But is that all we need to know?
Probably no! As we indulge more in chemistry, we can see, there are many more things related to CO2. To learn all those things smoothly we need to know about this gas in more detail.
So without further adieu, let’s quickly jump into the “ Carbon dioxide world”!!
This gas has a different use in different fields. From being used as a refrigerant to carbonated beverages, CO2 is everywhere. We must not forget how important it is for the plants!!
It is used in different industries as well.
The molar mass of CO2 is 44.009 g/mol and density is 1562 Kg/m3. Now let us learn the basic concepts about CO2 molecules.
CO2 Lewis Structure
The lewis structure of CO2 can be with some simple steps, but before that, it is important to understand lewis structure properly.
So lewis structure generally gives us an idea about the nature of bonding and octet fulfillment of the atoms. According to the octet rule, an atom attains stability by fulfilling its octet.
For example, in CO2, carbon needs 6 electrons to fulfill the octet, whereas oxygen needs only 2 electrons.
Now, let us quickly go through the steps for creating a lewis structure of any compound.
Step 1 – First and foremost we need to calculate the total valence electrons present in the molecule. Care should be taken regarding +, – signs. A ‘+’ sign means losing electrons and ‘-‘ means gaining.
Step 2 – Next we need to figure out the central atom of the molecule. Mostly the atom with the highest bonding sites is the central atom.
Step 3 – Next step will be, creating a skeleton containing only single bonds.
Step 4 – Then we need to complete the octet of the atoms with the electrons left. It’s advisable, to begin with, the electronegative atoms and then the electropositive ones.
Step 5 – After that, we need to ensure if there is a requirement of multiple bonds for fulfilling the octet rule of all atoms.
Step 6 – At the end ensure all the atoms are in their lowest possible formal charge. The calculation for formal charge can be done using the formula given below:-
Now let’s move on to the lewis structure of CO2,
Number of valence electrons of carbon = 4
Number of valence electrons of oxygen = 6
Number of valence electrons for 2 oxygen atoms = 6*2 = 12
Total valence electron = 16
Now, while deciding the central atom, notice that carbon has the highest bonding sites. Thus carbon is the central atom of this molecule.
Following up the step and after drawing the skeletal diagram, we see that 4 electrons are used so far. Still, 12 electrons are remaining.
But, looking at the octet of atoms, observe that carbon’s octet is not fulfilled. Thus according to the rule, changing the lone pairs into double bonds is necessary.
Now, the remaining electrons will be 8. These 8 electrons are distributed among the surrounding atoms.
In the end, check that carbon and oxygen both are having 8 electrons. Also, both are having the lowest possible formal charge.
Thus the lewis structure of CO2 is formed using 4-5 simple steps!
The hybridization of CO2 is Sp. The carbon atom is Sp hybridized and oxygen atoms are Sp2, making the overall molecule Sp hybridized.
Hybridization can be understood by 2 methods, one by understanding the combination of the orbitals and 2nd by using a simple formula.
Let’s understand the theory first and then we can use the formula easily!
The ground state configuration of C = 1s2 2s2 2p2
And ground state configuration of O = 1s2 2s2 2p4
Now when the atoms reach their excited state, 1 electron from the 2s orbital of carbon jumps to vacant orbital 2p. Thus new configuration becomes – 1s2 2s1 2p3
This leads to the formation of 2 Sp orbital involving one electron of 2s and 1 electron of 2p orbital of the carbon atom. The p orbitals of oxygen combine with the hybrid orbitals formed and a sigma bond is formed.
This explains the theory of hybridization in CO2. Now let’s come to the exciting part! The formula!!
The formula to find the hybridization of any compound is,
H = ½ [ V+M-C+A]
H represents the hybridization, V represents the number of valence electrons, M represents the number of the monovalent atom, C represents the charge of the cation, and A represents the charge of the anion
Now if H is 2, then it’s Sp hybridization
Likewise, if H= 3, it indicates Sp2 hybridization.
In the same way, when H is 4, the molecule will show Sp3 hybridization
When H is 5, it will Sp4 hybridization
And, when H is 6, the molecule will show Sp3d2 hybridization.
No. of valence electrons of the center atom (V) = 4
Here, M = 0, because oxygen is a divalent atom.
As CO2 is a neutral molecule, C and A will be 0 here.
Finally, H = ½ 
= 2 = Sp hybridization
These two ways are commonly used to understand the hybridization of CO2.
CO2 Molecular Geometry
CO2 has a linear shape. The bond angle of CO2 is 180°.
The molecular geometry of any compound can be determined by the VSEPR theory. The VSEPR chart is attached below, which will give us an idea about this.
So from the above chart, it’s clear that CO2 is an AX2 type molecule, where X= bonded atom
Thus the molecular geometry of the CO2 molecule will be linear.
The electron geometry of CO2 is linear as well. Before you bombard me with questions about electron geometry, let me clear it out!!
So molecular geometry is those which include only the atom while determining the shape of the molecule. Whereas electron geometry includes all electron pairs.
Likewise, electron geometry will include the lone pairs as well, which creates the difference between these two types of geometry.
CO2 doesn’t have any lone pair, so both geometries are the same in this case.
Let’s move on to the molecular orbital diagram of this compound.
CO2 Molecular Orbital (MO) Diagram
The molecular orbital diagram of CO2 is as below.
A molecular orbital diagram of any compound gives us an idea about the bonding of the orbitals. It also helps us to find the bond order, bond length, bond strength of the molecule.
In the diagram, the left-hand side consists of the atomic orbitals of carbon. Likewise, the left side has AO’s of oxygen. And in the middle is the MO.
We can see that the 2s orbital of oxygen is not involved in mixing and remains a nonbonding orbital. The reason for this is the high energy difference between the orbitals of carbon and the 2s orbital of oxygen.
All the 16 electrons are filled precisely as per rules. The antibonding orbitals are vacant in the case of CO2 as observed from the MO diagram.
Apart from these concepts, let us also study the methods of formation of CO2 gas.
The CO2 molecule is linear in shape and therefore both oxygen atoms have equal influence on the charge making CO2 a nonpolar molecule.
The molecule does not exhibit any polarization because of no dipole moment generated across the molecule.
For more detailed information, you can also refer to the article on CO2 polarity.
Process 1- CO2 is produced when calcium carbonate is reacted with hydrochloric acid.
2HCl + CaCO3 ——–> CO2 + CaCl2 + H2O
This is the easiest method used in the laboratory for CO2 formation.
Process 2 – Another way is the combination of methane and oxygen.
CH4 + 2O2 ——-> CO2 + 2H2O
This method indicates that all the carbon-based fuels can produce CO2 by the process of combustion.
Process 3 – 3rd process used to prepare CO2 is the thermal decomposition of CaCO3.
CaCO3 ——-> CaO + CO2
Calcium carbonate is heated at about 850℃ in this process. The CaO formed in this process is known as quick lime and is also used widely in industries.
Process 4 – Carbonic acid is used to produce CO2. The decomposition of this acid leads to the formation of CO2 and water.
H2CO3 ——–> CO2 + H2O
This process is widely used in industries because the formation of foam or bubbles, due to the release of CO2, neutralizes the waste acid streams.
Process 5 – Fermentation of different alcoholic beverages, like beer, whisky, leads to CO2 formation as a by-product.
C6H12O6 ———> 2CO2 + 2C2H5OH
Process 6 – The Respiration process of glucose releases CO2 and water as products.
C6H12O6 + 6O2 ——-> 6CO2 + 6H2O
Next, we need to know about the lewis structure, geometry, and hybridization of CO2.
As I said earlier, to understand the use of carbon dioxide smoothly, we need to learn the background of this gas beforehand. This background involves lewis structure, hybridization, molecular geometry, and molecular orbital diagram.
All the available details about these topics are jotted down in this article.
After this, you can easily go through any other topic related to CO2. I hope at the end of this article you get the answers to your long searched questions!! Have a happy learning.
If there is any question in any of the above concepts, feel free to ask me anytime.