Acetaldehyde (C2H4O) Lewis structure, Isomers, molecular geometry or
shape, hybridization, polar or nonpolar
The molecular formula C2H4O is used for representing three different isomers in chemistry i.e., ethylene oxide, acetaldehyde, and, vinyl alcohol or ethanol. Isomers are chemical compounds with the same molecular formula but a different structural representation.
In this article, we will learn about the chemistry of C2H4O isomers, molecular geometry, electron geometry, hybridization, formal charges, polarity nature, etc.
But first of all, we need to learn how to draw the Lewis structure of C2H4O.
The Lewis structure of acetaldehyde (C2H4O) is made up of 2 carbon (C) atoms present at the center while 4 hydrogens (H) and 1 oxygen (O) atom occupy terminal positions. According to the central C-atom, there are a total of 3 electron density regions around the central atom and it has no lone pair of electrons.
Drawing the Lewis dot structure of C2H4Ois quite easy if you follow the following simple steps.
Steps for drawing the Lewis dot structure of C2H4O
1. Count the total valence electrons in C2H4O
The Lewis dot structure of a molecule is referred to as a simplified representation of all the valence electrons present in it. Therefore, the very first step while drawing the Lewis structure of C2H4O is to count the total valence electrons present in the concerned elemental atoms.
As carbon (C) is present in Group IV A of the Periodic Table so it has 4 valence electrons. Oxygen (O) is present in Group VI A so it has 6 valence electrons while hydrogen (H) lies at the top of the Periodic Table of elements with a single valence electron only.
∴ C2H4O has two carbon atoms, four hydrogen atoms, and one oxygen atom. So, the total valence electrons available for the C2H4O Lewis structure = 2(4) +4(1) +6 = 18valence electrons.
2. Choose the central atom
Hydrogen has only 1 valence electron so it can only form a single bond thus it is never chosen as the central atom in a Lewis structure.
Carbon is less electronegative than oxygen so it is more likely to share its electrons with other atoms in its vicinity. Thus, carbon (C) is chosen as the central atom in the C2H4O Lewis structure.
Anyone C atom out of the two available can be placed at the center while the H and O atoms occupy terminal positions, as shown below.
3. Connect outer atoms with the central atom
In this step, we need to join the outer O and H atoms with the central C atoms using single straight lines. The two central C atoms are also joined to each other via single bonds, as shown below.
Each straight line represents a bond pair containing 2 electrons.
There are a total of 6 straight lines in the diagram above which means 6(2) = 12 valence electrons are used out of the 18 available.
Total valence electrons available – electrons used in bonding = 18-12 = 6 valence electrons.
So, we still have 6 valence electrons to be placed in the Lewis structure of C2H4
4. Complete the duplet and/or octet of the outer atoms
In the above Lewis structure, each hydrogen (H) atom already has a complete duplet with a total of 2 valence electrons in each.
On the other hand, the oxygen (O) atom requires 6 more electrons to achieve a stable octet electronic configuration, so these 6 valence electrons are placed as 3 lone pairs on the outer O-atom in the C2H4O Lewis structure.
You should also note that the octet of one central C-atom is also complete with a total of 4 single bonds around it i.e., 4(2) = 8 valence electrons.
Now we just need to complete the octet of the other C-atom present at the center.
5. Complete the octet of the central atom
The other C-atom present at the center has a total of 3 single bonds around it which denotes 6 valence electrons only. So, it still needs 2 more electrons to complete its octet configuration.
Thus, a lone pair present on the outer O-atom is converted into a covalent bond between the central C and the terminal O as shown below.
Now both the central C atoms have a complete octet with 4 single bonds around one C-atom and 2 single bonds and a double bond around the other C-atom.
Now let’s check the stability of this Lewis structure using the formal charge concept.
6. Check the stability of the C2H4O Lewis structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charge can be calculated using the formula given below.
Zero formal charges present on all the bonded atoms in the C2H4O molecule mark the stability of its Lewis structure.
But as we already mentioned at the beginning of this article that the molecular formula C2H4O represents three different isomers. So apart from the Lewis structure obtained above, there are two other possibilities for drawing the C2H4O Lewis structure, that we have discussed in the next section.
The Lewis structure of C2H4O shown below is that of acetaldehyde also called ethanal. It has an aldehyde CHO functional group at a terminal position.
The Lewis structure of C2H4O can also be shown in the figure below. It is an isomer of acetaldehyde known as ethylene oxide. It has a formyl C-O-C functional group at the center of the molecule. It is a three-membered ring cyclic ether.
The Lewis structure of C2H4O can also be represented as shown in the figure below. It represents ethenol or vinyl alcohol with a C=C double bond at the center and an alcohol OH functional group at a terminal position.
Acetaldehyde, ethylene oxide, and ethenol (or vinyl alcohol) are functional group isomers with the same molecular formula but different functional groups therefore they have three different Lewis structures.
What are the electron and molecular geometry of C2H4O?
C2H4O has an identical electron and molecular geometry or shape i.e., trigonal planar. The carbon atom bonded to the oxygen atom via a double bond is considered as the central atom while determining the shape and geometry of the molecule.
There is no lone pair of electrons on the central C-atom in C2H4O therefore the molecule experiences no distortion in its shape and geometry.
An easy way to find the shape and geometry of the molecule is to use the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the geometry or shape of a molecule using the VSEPR concept.
AXN notation for C2H4O molecule
A in the AXN formula represents the central atom. In the C2H4O molecule, carbon is present at the centre so A=C.
X denotes the atoms bonded to the central atom. In C2H4O, one oxygen (O) atom is bonded to the central C-atom on one side, a hydrogen (H) is attached on the other side while a CH3 group is attached on the third end. The CH3 group is considered 1 region of electron density in this molecule. In short X=3 for C2H4
N stands for the lone pairs present on the central atom. As per the Lewis structure of the C2H4O molecule, there is no lone pair on central C so N=0.
Hence, the AXN generic formula for the C2H4O molecule is AX3.
Now, you may have a look at the VSEPR chart below.
According to this chart, a molecule with an AX3 generic formula has a trigonal planar electron and molecular geometry or shape, as we already noted down for the C2H4O molecule.
Hybridization of C2H4O
The hybridization present in a molecule can be determined from the steric number of the central atom of the molecule.
The steric number of central C-atom in C2H4O is 3 so it has sp2 hybridization.
Refer to the figure and table given below.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
Is C2H4O polar or nonpolar?
Acetaldehyde (C2H4O) is a polar molecule. There is a small electronegativity difference between the bonded C and H atoms in C2H4O however an electronegativity difference of greater than 0.5 units exists between a C and an O atom.
Therefore, the oxygen atom present in the C2H4O molecule attracts each C-H electron cloud in addition to attracting the C=O electron cloud. The electron cloud stays non-uniformly distributed in the molecule overall. Thus it is polar with net µ > 0.
There are three possible Lewis structures for C2H4O, as shown below. Each of the following Lewis structures displays a total of 18 valence electrons.
The two carbon atoms are present at the center while oxygen and hydrogen atoms occupy terminal positions in each C2H4O Lewis structure.
These three Lewis structures represent isomeric compounds with the same molecular formula but a different structural arrangement of atoms.
How many bond pairs and lone pairs are present in the acetaldehyde (C2H4O) Lewis structure?
There are a total of 18 valence electrons i.e., 18/2 = 9 electron pairs in the acetaldehyde (C2H4O) Lewis structure.
Out of these 9 electron pairs, there are 7 bond pairs and 2 lone pairs.
Both the lone pairs of electrons are present on the terminal O-atom while no lone pair is present on any of the C and/or H-atoms.
How many possible isomers of C2H4O are there?
There are three possible and most stable isomers of C2H4O i.e., acetaldehyde, ethylene oxide, and vinyl alcohol. In a reaction mixture, vinyl alcohol stays in equilibrium with acetaldehyde.
The total number of valence electrons in the acetaldehyde (C2H4O) Lewis dot structure is 18.
There are three different isomers represented by the C2H4O molecular formula i.e., acetaldehyde, ethylene oxide, and vinyl alcohol (or ethenol).
The molecular geometry or shape of C2H4O is identical to its ideal electron pair geometry i.e., trigonal planar.
The Lewis structure of acetaldehyde (C2H4O) is made up of 2 carbon (C) atoms present at the center while 4 hydrogens (H) and 1 oxygen (O) atom occupy terminal positions.
C2H4O has sp2 hybridization with respect to the central C-atom.
C2H4O is a polar molecule with a net dipole moment µ>0.
The absence of any formal charges on the C2H4O atoms marks the stability of its Lewis structure.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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