Cyclohexane (C6H12) Lewis dot structure, molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polar vs nonpolar
Cyclohexane is a cyclic saturated hydrocarbon, represented by the chemical formula C6H12. It is a flammable, colorless liquid with a distinct odor.
Cyclohexane (C6H12) is primarily derived from petroleum and used as a solvent in producing plastics, adhesives, varnishes, lacquers, etc. Cyclohexane is also used for extracting essential oils from plants.
In this article, you will learn all about the Lewis structure of cyclohexane (C6H12), its molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polarity, etc.
Cyclohexane (C6H12) Lewis structure comprises a total of six carbon (C) atoms and twelve hydrogen (H) atoms. The C-atoms are arranged in a symmetrical, hexagonal ring arrangement, forming C-C-C single covalent bonds. Each C-atom is individually bonded to two hydrogen (H) atoms outside the ring.
Drawing the Lewis dot structure of C6H12 may seem tricky at first, but you can easily learn to draw it by following the simple steps given below.
Steps for drawing the Lewis dot structure of C6H12
1. Count the total valence electrons present in C6H12
The two distinct elements present in C6H12 are hydrogen and carbon.
Hydrogen (H) lies at the top of the Periodic Table of Elements, possessing a single valence electron only.
Carbon (C) is present in Group IV A (or 14) of the Periodic Table, with 4 valence electrons in each atom.
Total number of valence electrons in hydrogen = 1
Total number of valence electrons in carbon = 4
The cyclohexane (C6H12) molecule comprises 6 C-atoms and 12 H-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of C6H12 = 6(4) + 12(1) = 36 valence electrons.
2. Choose the central atoms
Out of the two different types of atoms present in cyclohexane, hydrogen cannot be chosen as the central atom.
An H-atom can accommodate a total of 2 valence electrons, forming a single covalent bond with 1 adjacent atom only.
Therefore, the only option left is carbon.
There are 6 C-atoms in C6H12. All six atoms are equivalent. Hence, these are arranged as a hexagon in the C6H12 Lewis dot structure.
Any one C-atom can be considered a central atom, while the 12 H-atoms are spread around these, as shown below.
3. Connect the outer H-atoms with the adjacent C-atoms
In this step, each outer H-atom is joined to its adjacent C-atom using single straight lines.
In this way, each C-atom is individually bonded to 2 H-atoms, as shown below.
4. Connect the central C-atoms with each other
Now the six C-atoms are joined to each other, forming a hexagonal ring arrangement, as shown below.
A straight line represents a single covalent bond containing 2 valence electrons.
There are a total of 18 single bonds in the cyclohexane Lewis structure drawn so far. This means 18(2) = 36 valence electrons are already consumed.
5. Ensure that all the C-atoms in the hexagonal ring have a complete octet
Total valence electrons used till step 4 = 18 single bonds = 36 valence electrons.
Total valence electrons – electrons used till step 4 = 36 – 36 = 0 valence electrons.
As all the valence electrons initially available for drawing the C6H12 Lewis structure are already consumed, therefore there is no lone pair on any of the hexagonally arranged C-atoms.
Also, all 6 C-atoms have a complete octet as per 4 single bonds, i.e., 4(2) = 8 valence electrons surrounding it.
This means we don’t need to make any changes w.r.t the C-atoms in the above structure.
Now let’s move ahead and check its stability by applying the formal charge concept.
6. Check the stability of Lewis’s 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 charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the C6H12-bonded atoms.
Non-bonding electrons = no lone pair = 0 electrons
Formal charge = 4-0-8/2 = 4-0-4 = 4-4 = 0
For each hydrogen atom
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 or no formal charges on either of the atoms present in C6H12 mark the incredible stability of the cyclohexane Lewis dot structure obtained below.
However, an interesting fact is that, in reality, a cyclohexane molecule adopts the following conformations.
These conformational isomers are interconvertible structures produced by the continuous rotation of the sigma bonds present in cyclohexane at room temperature.
Cyclohexane (C6H12) adopts different conformations to lower its energy and thus gain greater stability. The chair conformation of C6H12 is the most stable (on account of its lowest energy content), while the half-chair form is the least stable structure (having max. energy).
What are the electron and molecular geometry of C6H12?
The molecular geometry or shape of cyclohexane (C6H12) w.r.t each C-atom is identical to its ideal electronic geometry, i.e., tetrahedral. To a C-atom at the center, 2 H-atoms and 2 other C-atoms are directly attached. The central C-atom has no lone pairs of electrons; thus, no distortion is witnessed in the overall shape and geometry of C6H12.
Molecular geometry of C6H12
The molecular geometry or shape of cyclohexane (C6H12) w.r.t each C-atom is tetrahedral.
In the hexagonal ring arrangement of cyclohexane, each C-atom is covalently bonded to two hydrogen atoms and two other carbon atoms like four corners of a tetrahedron. There are no lone pairs of electrons on this C-atom. Hence no lone pair-lone pair or lone pair-bond pair electronic repulsions exist in the molecule.
This results in an overall symmetrical hexagonal ring arrangement and a tetrahedral molecular shape of cyclohexane w.r.t each C-atom, as shown below.
Electron geometry of C6H12
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 C6H12, each C-atom is surrounded by 4 bond pairs (i.e., 2 C-C bonds and 2 C-H bonds), and it has no lone pair of electrons, making a total of 4 electron density regions only.
Hence, the ideal electron pair geometry of cyclohexane (C6H12) w.r.t each C-atom is also tetrahedral.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs present on the central atom.
It is used to predict the shape and geometry of a molecule using the VSEPR concept.
AXN notation for cyclohexane (C6H12)
A in the AXN formula represents the central atom. In C6H12, a carbon (C) atom is present at the center, so A = C.
X denotes the atoms bonded to the central atom. In C6H12, 2 H-atoms and 2 C-atoms are directly bonded to the central C-atom. So X = 4 for C6H12.
N stands for the lone pairs present on the central atom. As per the Lewis structure of C6H12, the central C-atom has no lone pair of electrons. Thus, N = 0 for C6H12.
As a result, the AXN generic formula for C6H12 w.r.t each C-atom is AX4N0or simply AX4.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that a molecule with AX4 generic formula possesses an identical electron and molecular geometry or shape, i.e., tetrahedral, as we already noted down for cyclohexane (C6H12).
Hybridization of C6H12
Each C-atom is sp3 hybridized in cyclohexane (C6H12).
The electronic configuration of carbon (C) is 1s2 2s2 2p2.
During chemical bonding in C6H12, the 2s electrons of carbon get unpaired, and one of these electrons shifts to an empty 2p atomic orbital.
The half-filled 2s atomic orbital of carbon thus hybridizes with its three half-filled 2p orbitals to produce four sp3 hybrid orbitals.
Each sp3 hybrid orbital possesses a 25 % s-character and a 75 % p-character. All the sp3 hybrid orbitals are equivalent in cyclohexane, containing a single unpaired electron only.
Thus, the six C-atoms form C-C and C-H sigma bonds by overlapping with the sp3 and s atomic orbitals of adjacent carbon and hydrogen atoms, respectively, as shown below.
Another shortcut to finding the hybridization present in a molecule is using its steric number against the table given below.
The steric number of each C-atom in C6H12 is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of C6H12
The ideal bond angle in a symmetrical tetrahedral shape is 109.5°. Therefore, each C-C-C, C-C-H and H-C-H bond angle equals 109.5° in cyclohexane (C6H12).
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms having an electronegativity difference between 0.4 to 1.6 units.
The C-C bonds present in cyclohexane are purely non-polar as they are formed between two identical carbon atoms having zero or no electronegativity differences.
In contrast, a small electronegativity difference of 0.35 units is present between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom in each C-H bond of C6H12.
0.35 units < 0.4 units. Therefore, the C-H bond is also considered non-polar, as per Pauling’s electronegativity scale.
But considering the fact that it is formed between two dissimilar atoms, so the slightly more electronegative C-atom attracts the C-H electron cloud to a minutely greater extent. Oppositely charged dipoles develop in the cyclohexane molecule.
However, it is due to the symmetrical hexagonal molecular arrangement and tetrahedral shape w.r.t each C-atom that the charged electron cloud stays uniformly distributed overall in C6H12.
The individual C-H dipole moments get canceled equally, making cyclohexane (C6H12) a non-polar molecule overall (net µ = 0).
The Lewis dot structure of cyclohexane (C6H12) displays a total of 36 valence electrons, i.e., 36/2 = 18 electron pairs.
All 18 electron pairs are bond pairs which mean there is no lone pair of electrons in C6H12.
6 C-atoms are hexagonally arranged in C6H12 via C-C single covalent bonds.
Each C-atom is single covalently bonded to 2 H-atoms outside the hexagonal ring.
In this way, there are 6 C-C bond pairs and 12 C-H bond pairs in the C6H12 Lewis structure.
How is the Lewis structure of benzene (C6H6) different from that of cyclohexane (C6H12)?
The Lewis structure of benzene (C6H6) contains 6 hexagonally arranged carbon atoms. There are 3 C-C single and 3 C=C double covalent bonds at alternate positions. Each C-atom is individually bonded to 1 H-atom outside the ring.
Therefore, the Lewis structure of C6H6 is different from that of cyclohexane (C6H12), containing 6 C-C single bonds and 2 H-atoms are directly bonded to each C-atom outside the hexagonal ring.
What is the molecular shape of C6H12?
The molecular geometry or shape of cyclohexane (C6H12) w.r.t each C-atom is tetrahedral.
The central C-atom is directly bonded to 2 other C-atoms and 2 H-atoms, making a total of 4 electron density regions thus, no electronic repulsions or molecular distortion occurs in C6H12.
How is the shape of C6H6 different from that of C6H12?
The VSEPR shape of C6H12w.r.t each C-atom is tetrahedral.
In contrast, the molecular shape of C6H6w.r.t each C-atom is trigonal planar. One C-atom is directly bonded to 2 other C-atoms and 1 H-atom, respectively, like three corners of an equilateral triangle. However, both benzene (C6H6) and cyclohexane (C6H12) possess similar hexagonal rings.
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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