Ethanol (C2H5OH) Lewis structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, isomers, polar or nonpolar
C2H5OHis the chemical formula for ethanol, also known as ethyl alcohol, primary alcohol. The IUPAC name for ethanol is ethan-1-ol because the hydroxyl (OH) functional group is attached at carbon no.1.
In this article, we are going to explore interesting facts about C2H5OH, including how to draw its Lewis dot structure, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, isomers, polarity, etc.
So, what are you waiting for? Dive into the article, and let’s start reading! Happy learning.
The Lewis structure of ethanol (C2H5OH) consists of three different elemental atoms, i.e., two carbon (C) atoms, six hydrogen (H) atoms and one atom of oxygen (O).
There are two C-atoms, single-bonded to each other at the centre. One C-atom is bonded to three H-atoms, while the other C-atom is bonded to two H-atoms and a hydroxyl (OH) functional group.
In this way, each C-atom has a total of four electron density regions around it. All four electron density regions or electron domains are constituted of bond pairs. Hence there is no lone pair of electrons on any one C-atom in the C2H5OH Lewis dot structure.
You can easily learn to draw the Lewis dot structure of C2H5OH by following the simple steps given below.
Steps for drawing the Lewis dot structure of C2H5OH
1. Count the total valence electrons in C2H5OH
The very first step while drawing the Lewis structure of C2H5OH is to calculate the total valence electrons present in its concerned elemental atoms.
As three different elemental atoms are present in C2H5OH, so you first need to look for the position of these elements in the Periodic Table.
Carbon (C) belongs to Group IV A (or 14), so it has a total of 4 valence electrons. Oxygen (O) is present in Group VI A (or 16), so it has 6 valence electrons, while hydrogen (H) lies at the top of the Periodic Table containing a single valence electron only.
∴ The C2H5OH molecule consists of 2 C-atoms, 1 O-atom, and 6 H-atoms. Therefore, the total valence electrons available for drawing the Lewis dot structure of C2H5OH = 2(4) + 1(6) + 6(1) = 20 valence electrons.
2. Choose the central atom
In this second step, usually the least electronegative atom out of all the concerned atoms is chosen as the central atom.
This is because the least electronegative atom is the one that is most likely to share its electrons with the atoms spread around it.
Oxygen (E.N = 3.44) is more electronegative than both carbon and hydrogen. Hydrogen (E.N = 2.20) is less electronegative than carbon (E.N = 2.55). Still, it cannot be chosen as the central atom because a hydrogen (H) atom can accommodate only 2 electrons which denotes it can form a bond with a single adjacent atom only. This denotes that H is always placed as an outer atom in a Lewis structure.
Consequently, both C-atoms are placed at the center of the C2H5OH Lewis structure while the O-atom and the H-atoms are spread around them, as shown below.
3. Connect outer atoms with the central atom
In this step, the central C-atoms are joined to each other via single straight lines. Each C-atom is then joined to its neighboring outer atoms, as shown below.
You must also remember that an H-atom present next to the O-atom is only joined to the oxygen atom and not to any C-atom at the center. This is because an H-atom can form a single bond with one adjacent atom only in any Lewis structure.
An oxygen atom is highly electronegative, so it readily forms a covalent chemical bond with its adjacent H-atom, not allowing the latter a chance to form a direct C-H bond.
A single straight line represents a bond pair containing 2 electrons. There are a total of 8 single bonds in the above structure representing 8(2) = 16 valence electrons. Hence, 16 valence electrons are already consumed out of the 20 initially available for drawing the C2H5OH Lewis structure.
4. Complete the duplet and/or octet of the outer atoms
As we already identified, the hydrogen and oxygen atoms are the outer atoms in the Lewis dot structure of C2H5OH.
Each hydrogen (H) atom requires a total of 2 valence electrons in order to achieve a stable duplet electronic configuration.
A C-H and an O-H single bond already represent 2 valence electrons around each H-atom. This means all six H-atoms already have a complete duplet in the Lewis structure drawn till yet. Thus, we do not need to make any changes with regard to the hydrogen atoms in this structure.
In contrast to that, an O-atom needs a total of 8 valence electrons to achieve a stable octet electronic configuration.
A C-O bond and an O-H bond represent 2(2) = 4 electrons which denote that the outer O atom needs 4 more electrons to complete its octet. Consequently, these 4 valence electrons are placed as 2 lone pairs on the oxygen (O) atom in the C2H5OH Lewis structure, as shown below.
5. Complete the octet of the central atom
In the Lewis structure obtained till step 4, each central C-atom has a total of 4 single bonds around it. Four single covalent bonds represent a total of 8 valence electrons around each C-atom. Thus, both carbon atoms already have a complete octet electronic configuration.
Total valence electrons used till step 4 = 8 single bonds + electrons placed around the O-atom, shown as dots = 8(2) + 4 = 20 valence electrons.
Total valence electrons – electrons used till step 4 = 20 – 20 = 0 valence electrons.
As all the valence electrons initially available for drawing the C2H5OH Lewis structure are already consumed hence there is no lone pair of electrons on any one C-atom at the center.
As a final step, we need to check the stability of the C2H5OH Lewis structure, which can be done by using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The fewer formal charges present on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
The absence of any formal charges on the bonded atoms in the C2H5OH Lewis structure ensures that it is a stable Lewis representation of ethanol, and thus we have drawn it correctly.
An isomer of the above structure is the structure given below. It is known as dimethyl ether. Ethanol and dimethyl ether are functional group isomers. Isomers are chemical compounds having the same molecular formula but a different structural arrangement.
Both ethanol and dimethyl ether are represented by C2H6O (the same molecular formula). However, ethanol is an alcohol represented by a hydroxyl (OH) functional group at the terminal position. Contrarily, an ether (-O-) functional group is present in dimethyl ether, so their structural arrangement is entirely different.
Now that we have learned everything about C2H5OH structure, let us proceed forward and discuss its molecular and electron geometry.
What are the electron and molecular geometry of C2H5OH (Ethanol)?
The ethanol (C2H5OH) molecule has an identical electron and molecular geometry or shape, i.e., tetrahedral.
To avoid confusion, anyone C-atom can be considered a central atom while determining the shape and geometry of C2H5OH. With respect to both C-atoms, there are a total of four electron density regions around them.
All four electron density regions or electron domains are comprised of bond pairs, and there is no lone pair on the central C-atom, so its shape and geometry stay undistorted.
Molecular geometry of C2H5OH
The molecular geometry or shape of ethanol (C2H5OH) is tetrahedral.
The absence of any lone pair of electrons on the central C-atom means no lone pair-lone pair and lone pair-bond pair electronic repulsions exist in the molecule.
A bond pair-bond pair repulsive effect is present, which makes the bonded electron pairs occupy the four corners of a tetrahedron, as shown in the figure below.
Electron geometry of C2H5OH
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In C2H5OH, carbon no. 1 has three H-atoms and a CH2OH functional group around it. Conversely, carbon no. 2 has two H-atoms, a hydroxyl (OH) functional group and a methyl (CH3) group. The CH2OH, OH and CH3 groups are considered one region of electron density each while determining the shape and geometry of the molecule.
In short, there are a total of 4 electron density regions around the central C-atom with respect to both C-atoms in C2H5OH. Hence its electron geometry with respect to both C-atoms is tetrahedral.
A shortcut to finding the electron and the molecular geometry of a molecule is by using 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 shape and geometry of a molecule based on the VSEPR concept.
AXN notation for C2H5OH molecule
A in the AXN formula represents the central atom. In C2H5OH, a carbon (C) atom is present at the center, so A = C.
X denotes the atoms bonded to the central atom. In C2H5OH, three hydrogens (H) atoms and a CH2OH group is directly bonded to the central C-atom. The CH2OH group is considered 1 region of electron density. In short, X = 3 + 1 = 4 for C2H5OH.
N stands for the lone pairs present on the central atom. As per the Lewis structure of C2H5OH, there are no lone pairs of electrons on the central carbon; hence N = 0.
As a result, the AXN generic formula for C2H5OH is AX4.
Now, you may have a quick look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX4 generic formula is identical to its ideal electron pair geometry, i.e., tetrahedral, as we already noted down for ethanol (C2H5OH).
Hybridization of C2H5OH
Both central C-atoms are sp3 hybridized in C2H5OH.
The electronic configuration of carbon is 1s2 2s2 2p2.
During chemical bonding, the 2s atomic orbital of carbon hybridizes with its three half-filled 2p atomic orbitals to produce four sp3 hybrid orbitals.
Each sp3 hybrid orbital is equivalent and contains a single electron only. It possesses a 25% s-character and a 75% p-character.
The sp3 hybrid orbitals of carbon overlap with the atomic orbitals of adjacent atoms to form the required sigma (σ) bonds, as shown below.
C2H5OH hybridization can also be determined from its steric number. The steric number of a central C-atom in C2H5OH is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The Ethanol (C2H5OH) bond angle
The bonded atoms form an ideal bond angle of 109.5° due to the symmetrical tetrahedral shape of C2H5OH (Ethanol), as shown below.
Oxygen is a highly electronegative element. A large electronegativity difference of 0.89 units exists between the bonded carbon and oxygen atoms in a C-O bond.
Similarly, an even higher electronegativity difference of 1.24 units exists between the bonded oxygen and hydrogen atoms in the O-H bond present in C2H5OH.
The oxygen atom not only attracts the shared electron cloud of the C-O and O-H bonds but also attracts electrons from each C-H bond. A non-uniform electron cloud distribution in the molecule contributes to the highly polar characteristics of ethanol. An ethanol molecule has a high net dipole moment (µ = 1.69 Debye).
It can even form strong hydrogen bonding using its OH group, which is why ethanol is an extremely well-appreciated polar solvent.
The Lewis dot structure of ethanol (C2H5OH) displays a total of 20 valence electrons i.e., 20/2 = 10 electron pairs.
Two carbon (C) atoms, single-bonded to each other at the center, are simultaneously bonded to three H-atoms on one side and two H-atoms, and an OH functional group on the other side.
Out of the 10 electron pairs, there are 8 bond pairs and 2 lone pairs of electrons.
Both the lone pairs are situated on the oxygen atom, while there is no lone pair on any of the C or H-atoms.
There are 8 sigma and no pi bonds present in C2H5OH. This is because C2H5OH is a saturated molecule. There are all C-C, C-H, C-O, and O-H single covalent bonds present in it.
The absence of any double or triple bond signifies there are no pi-bonded electrons in a C2H5OH molecule.
What is the number of atoms present in C2H5OH?
A total of 9 atoms are present in an ethanol (C2H5OH) molecule. Out of the 9 atoms, there are 2 C-atoms, 6 H-atoms, and 1 O-atom. Therefore, the molecular formula for C2H5OH is C2H6O.
What is the molecular geometry of C2H5OH?
The molecular geometry or shape of C2H5OH is tetrahedral. Around one atom at the center, a total of four different types of bonds are present.
How is the shape of C2H5OH different from its ideal electron pair geometry?
The ethanol (C2H5OH) molecule has a shape identical to its ideal electron pair geometry. The AXN generic formula for C2H5OH is AX4, so it has a tetrahedral shape and electron geometry as per the VSEPR concept.
How do you compare the shapes of two alcohols: ethanol (C2H5OH) and methanol (CH3OH)?
Both ethanol (C2H5OH) and methanol (CH3OH) are primary alcohols, possessing the same tetrahedral shape and molecular geometry with respect to the central carbon atom.
The total number of valence electrons available for drawing ethanol (C2H5OH) Lewis structure is 20.
C2H5OH has an identical electron and molecular geometry or shape, i.e., tetrahedral.
The C2H5OH molecule has sp3 hybridization.
The bonded atoms form a mutual bond angle of 109.5° in the tetrahedral C2H5OH molecule.
C2H5OH is a polar molecule (net µ = 1.69 D).
Zero formal charges present on all the bonded atoms in the C2H5OH molecule account for the extraordinary stability of the Lewis structure drawn in this article.
Ethanol and dimethyl ether are two functional group isomers represented by the same molecular formula, i.e., C2H6.
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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