Ethane (C2H6) Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar vs non-polar
Anyone who has even a little bit of knowledge about organic chemistry, he or she must be familiar with ethane. Ethane is represented by the chemical formula C2H6 (molar mass = 30.07 g/mol).
You can revise everything you might already know about C2H6 through this article, such as how to draw its Lewis dot structure. In addition to that, you may also learn some new things about the molecular geometry or shape of C2H6, its electron geometry, bond angle, hybridization, formal charges, polarity, etc.
So, without any further delay, dive into the article, and let’s start reading!
The Lewis structure of ethane (C2H6) is made up of two carbon (C) atoms and six atoms of hydrogen (H). An anyone carbon atom can be considered a central carbon. With reference to this central C-atom, there are a total of 4 electron-density regions around it.
All four electron density regions are comprised of bond pairs. Thus, there is no lone pair of electrons on this central C-atom in the C2H6 Lewis dot structure.
Drawing the Lewis dot structure of ethane (C2H6) is quite an easy task if you follow the simple steps given below.
As carbon (C) is present in Group IV A (or 14) of the Periodic Table so it has 4 valence electrons while hydrogen (H) lies at the top of the Periodic Table of elements with a single valence electron only.
∴ C2H6 has two carbon atoms and six atoms of hydrogen. So, the total valence electrons available for drawing the C2H6 Lewis structure = 2(4) +6(1) = 14valence 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.
Hydrogen (E.N = 2.20) is less electronegative than carbon (E.N = 2.55) but it cannot be chosen as the central atom because a hydrogen (H) atom can accommodate only 2 valence electrons so 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.
In short, the two C-atoms are placed at the center while all the hydrogen atoms occupy terminal positions in the C2H6 Lewis structure, as shown below.
3. Connect outer atoms with the central atom
Now we need to connect the outer atoms with the central atom of the Lewis structure using single straight lines. So the two C-atoms are joined to the outer H-atoms using straight lines. Also, the two C-atoms are joined to each other, as shown in the diagram below.
Each straight line represents a single covalent bond i.e., a bond pair containing 2 electrons. There are a total of 7 single bonds in the above diagram.
As 7 (2) = 14, that means all the 14 valence electrons available for drawing the C2H6 Lewis structure are already consumed.
But do all the bonded atoms have a stable electronic configuration in this Lewis structure? Let’s check that in the next steps.
4. Complete the duplet and/or octet of the atoms
As we know that there are 6 H-atoms present as outer atoms in the ethane (C2H6) Lewis structure. Each H-atom needs a total of 2 valence electrons only in order to achieve a stable duplet electronic configuration.
The C-H single bonds represent that each H-atom already has 2 electrons in its vicinity which indicates a complete duplet. Therefore, we need not worry about the H-atoms in this structure.
Also, the good news is that both the central C-atoms have a stable octet electronic configuration with a total of 8 valence electrons (i.e., 3 C-H bonds + 1 C-C bond) surrounding each.
Conversely, both the C-atoms are equivalent with the same kind of bonding on each side, perfectly in line with what we told you at the beginning i.e., anyone C-atom can be considered a central atom while determining the Lewis structure, shape, and geometry of ethane.
With all that said, the final step is just to check the stability of this Lewis structure of C2H6 which can be done using the formal charge concept.
5. Check the stability of the C2H6 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.
Non-bonding electrons = no lone pairs = 0 electrons
Formal charge = 4-0-8/2 = 4-0-4 = 4-4 = 0
For hydrogen atoms
Valence electrons of hydrogen = 1
Bonding electrons = 1 single bond = 2 electrons
Non-bonding electrons = no lone pairs = 0 electrons
Formal charge = 1-0-2/2 = 1-0-1 = 1-1 = 0
Zero formal charges present on all the bonded atoms in the ethane (C2H6) molecule marks the incredible stability of the Lewis structure that we have drawn.
Now let’s move ahead and discuss other interesting facts about C2H6 including its shape, geometry, and hybridization.
What are the electron and molecular geometry of C2H6?
C2H6 has an identical electron and molecular geometry or shape i.e., tetrahedral. Considering any one carbon atom as the central atom, it is bonded to 3 H-atoms on one side and to a CH3 group on the other side.
In this way, there are a total of 4 electron density regions around the central C-atom and there is no lone pair of electrons on this atom. As a result, the ethane molecule experiences no distortion in its shape and geometry.
The 3 H-atoms and the CH3 group lie along the 4 vertices of a tetrahedron in a perfectly symmetrical manner, as shown in the figure below.
An easier way of finding the electron and the molecular geometry or shape 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 geometry or shape of a molecule using the VSEPR concept.
AXN notation for C2H6 molecule
A in the AXN formula represents the central atom. In the C2H6 molecule, carbon is present at the center so A=C.
X denotes the atoms bonded to the central atom. In C2H6, 3 hydrogens (H) are attached on one side while a CH3 group is attached on the other end of each carbon atom. The CH3 group is considered 1 region of electron density in this molecule. In short X= 3+1 = 4 for C2H6.
N stands for the lone pairs present on the central atom. As per the Lewis structure of the C2H6 molecule, there is no lone pair on central C so N=0.
Hence, the AXN generic formula for the C2H6 molecule is AX4.
Now, you may have a look at the VSEPR chart below.
According to this chart, a molecule with an AX4 generic formula has a tetrahedral electron and molecular geometry or shape, as we already noted down for the C2H6 molecule.
Hybridization of C2H6
The hybridization present in a molecule can be determined from the steric number of the central atom in the molecule.
The steric number of central C-atom in C2H6 is 4 so it has sp3 hybridization.
Refer to the figure and table given below.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The C2H6 bond angle
As the ethane molecule has a perfectly symmetrical tetrahedral shape and geometry thus the bonded atoms form a mutual bond angle of 109.5° in this molecule.
The C-C bond length is 153 pm while the C-H bond length is 108 pm in C2H6.
Ethane (C2H6) is a non-polar molecule. Zero electronegativity difference exists between two identical C-atoms at the center of the molecule. However, there is a small electronegativity difference of 0.35 units between the bonded C (E.N = 2.55) and H (E.N = 2.20) atoms in C2H6.
The central carbon atoms only slightly attract the shared C-H electron clouds from each side of the molecule.
However, it is due to the symmetrical tetrahedral shape of C2H6 that the small dipole moment (symbol µ) of oppositely pointing C-H groups get canceled equally.
The electron cloud stays uniformly distributed in the molecule overall. Thus ethane is a non-polar molecule with net µ =0.
The Lewis structure of ethane (C2H6) is shown below.
It displays a total of 14 valence electrons i.e., 14/2 = 7 electron pairs.
All 7 electron pairs are constituted of bond pairs including 1 C-C bond pair and 6 C-H bond pairs.
However, there is no lone pair of electrons on any of the C or H atoms in the C2H6 Lewis structure.
How many bonded pairs are there in the C2H6 compound?
There are a total of 7 bonded pairs in C2H6 including 1 C-C bond pair and 6 C-H bond pairs.
What is the molecular geometry of C2H6?
The ethane (C2H6) molecule has a tetrahedral molecular geometry or shape. It is identical to its electron pair geometry. There are a total of 4 electron density regions around the central C-atom in C2H6, constituted of 3 H-atoms and 1 CH3 group.
There is no lone pair of electrons on the central C-atom thus the generic AXN formula for C2H6 is AX4 and it is tetrahedral as per the VSEPR concept.
How is the molecular shape of C2H6 different from that of C2H2 and C2H4?
The ethane (C2H6) molecule has a tetrahedral shape.
The ethyne (C2H2) molecule has a linear shape. There are a total of 2 electron-density regions around the central C-atom in C2H2 made up of 1 H-atom and 1 CH group.
The ethene (C2H4) molecule has a trigonal planar shape. There are a total of 3 electron-density regions around the central C-atom in C2H4 comprising 2 H-atoms and 1 CH2 functional group.
C2H6 has a symmetrical tetrahedral shape. However, it is not a planar molecule because there are 3 identical H-atoms against 1 CH3 group. Thus, all the bonded atoms do not lie on the same plane and C2H6 is a non-planar molecule.
It is due to this non-planar arrangement that some online sources claim that the CH3– CH3 groups repel each other and in reality, the molecule adopts a trigonal pyramidal shape as opposed to the ideal tetrahedral shape. But this topic is debatable and out of the scope of this article.
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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