Benzene (C6H6) Lewis structure, molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polar or nonpolar
C6H6 is the chemical formula for a very versatile molecule, i.e., benzene, the parent member of the aromatic family. It is a colorless, highly flammable liquid that emits a sweet odor.
Benzene is widely used as a starting material in producing valuable chemicals, polymers, nanomaterials and pharmaceutical drugs inclusive.
This article is very important because here we have discussed how to draw the Lewis dot structure of benzene (C6H6), what is its molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polarity, etc.
The Lewis structure of benzene (C6H6) comprises a total of six carbon (C) atoms and six hydrogen (H) atoms. The C-atoms are arranged in a symmetrical, hexagonal ring arrangement. This hexagon contains 3 C-C single and 3 C=C double covalent bonds at alternate positions. Each C-atom is also bonded to a hydrogen (H) atom outside the ring.
You might find drawing the Lewis dot structure of benzene (C6H6) a bit tricky initially, but you can easily do so by following the simple steps below.
Steps for drawing the Lewis dot structure of C6H6
1. Count the total valence electrons present in C6H6
The two distinct elements present in C6H6 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,withf 4 valence electrons in each atom.
Total number of valence electrons in hydrogen = 1
Total number of valence electrons in carbon = 4
The benzene (C6H6) molecule comprises 6 C-atoms and 6 H-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of C6H6 = 6(4) + 6(1) = 30 valence electrons.
2. Choose the central atoms
Out of the two different types of atoms present in benzene, 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 C6H6. All six atoms are equivalent. Hence, these are arranged as a hexagon in the C6H6 Lewis dot structure.
Any one C-atom can be considered a central atom, while the 6 H-atoms are placed at peripheries, 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.
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.
Each straight line represents a single covalent bond containing 2 valence electrons.
There are a total of 12 single bonds in the benzene Lewis structure drawn so far. This means 12(2) = 24 valence electrons are already consumed out of the 30 initially available.
5. Place the remaining valence electrons on the C-atoms
Total valence electrons used till step 4 = 12 single bonds = 24 valence electrons.
Total valence electrons – electrons used till step 4 = 30 – 24 = 6 valence electrons.
These remaining 6 valence electrons are accommodated as 3 lone pairs, one on any of the three C-atoms in the benzene Lewis structure.
6. Complete the duplet and/or octet of all the atoms and convert lone pairs into covalent bonds if necessary
Each H-atom is surrounded by a C-H single covalent bond, i.e., 2 valence electrons. Thus, all the H-atoms already have a complete duplet in the C6H6 Lewis structure.
Contrarily, the C-atoms carrying a lone pair have a complete octet (8 valence electrons), while those without a lone pair are unstable.
Therefore, the lone pair from each C-atom is converted into an additional covalent bond between that C-atom and its neighbor, as shown below.
In this way, C=C double covalent bonds are present at alternating positions in the C6H6 Lewis structure, and all the C-atoms are identical and equivalent, with a complete octet electronic configuration.
Finally, we just need to check the stability of the Lewis structure obtained above. Let’s do that by applying the formal charge concept.
7. 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 6 to determine the formal charges present on the C6H6-bonded atoms.
For each carbon atom
Valence electrons of carbon = 4
Bonding electrons = 2 single bonds + 1 double bond = 2(2) + 4 = 8 electrons
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 C6H6 mark the incredible stability of the benzene Lewis dot structure obtained below.
However, you may note that the following resonance forms are possible for representing the benzene molecule.
Each resonance form is a way of representing the Lewis structure of a molecule. The pi-bonded electrons are delocalized, i.e., they keep revolving from one position to another on the molecule.
The actual benzene structure is a hybrid of all the representative resonance forms, in which the delocalized electron cloud is shown as a ring at the center.
Structures I and II are the most stable. These are known as the Kekule structures, and they contribute the most (80 %) in the resonance hybrid.
Contrarily, structures III-V known as the Dewar structures, contribute minimally (20%) in the benzene resonance hybrid.
Now that we know everything about the benzene Lewis structure, let’s move ahead and discuss the electron and molecular geometry or shape of the benzene molecule.
What are the electron and molecular geometry of C6H6 (Benzene)?
The molecular geometry or shape of benzene (C6H6) w.r.t each C-atom is identical to its ideal electronic geometry, i.e., trigonal planar. To a C-atom at the center, 1 H-atom and 2 other C-atoms are covalently attached. The central C-atom has no lone pairs of electrons; thus, no distortion is witnessed in its shape or geometry.
Molecular geometry of C6H6
The molecular geometry or shape of benzene (C6H6) w.r.t each C-atom is trigonal planar.
In the hexagonal ring arrangement of benzene, each C-atom is covalently bonded to one hydrogen atom and two carbon atoms, forming three corners of an equilateral triangle. 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 trigonal planar molecular shape of benzene w.r.t each C-atom, as shown below.
Electron geometry of C6H6
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 3 electron density regions around the central atom is trigonal planar.
In C6H6, each C-atom is surrounded by 3 bond pairs (C-H, C-C and C=C bonds), and it has no lone pair of electrons, making a total of 3 electron density regions only.
Hence, the ideal electron pair geometry of benzene w.r.t each C-atom is trigonal planar.
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 the benzene (C6H6) molecule
A in the AXN formula represents the central atom. In C6H6, a carbon (C) atom is present at the center, so A = C.
X denotes the atoms bonded to the central atom. In C6H6, 1 H-atom and 2 C-atoms are directly bonded to the central C-atom. So X =3 for C6H6.
N stands for the lone pairs present on the central atom. As per the Lewis structure of C6H6, the central C-atom has no lone pair of electrons. Thus, N = 0 for C6H6.
As a result, the AXN generic formula for C6H6 w.r.t each C-atom is AX3N0or simply AX3.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that a molecule with AX3 generic formula possesses an identical electron and molecular geometry or shape, i.e., trigonal planar, as we already noted down for the benzene (C6H6) molecule.
Hybridization of C6H6
Each C-atom is sp2 hybridized in benzene (C6H6).
The electronic configuration of carbon (C) is 1s2 2s2 2p2.
During chemical bonding in benzene, the 2s electrons of carbon get unpaired, and one of these electrons shifts to an empty 2p atomic orbital. This results in half-filled 2s and 2p atomic orbitals of carbon.
The 2s orbital hybridizes with two of the three 2p orbitals to produce three sp2 hybrid orbitals.
Each sp2 hybrid orbital possesses 33.3 % s-character and 66.7 % p-character. All the sp2 hybrid orbitals are equivalent in benzene, containing a single unpaired electron only.
Thus, the six C-atoms form C-C and C-H sigma bonds by overlapping with the sp2 and s atomic orbitals of adjacent carbon and hydrogen atoms, respectively.
In contrast, each C-atom uses its unhybridized p-orbital to form the C=C pi bond by the p-p orbital overlap in benzene.
Refer to the figure drawn 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 C6H6 is 3, so it has sp2 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of C6H6
The ideal bond angle in a symmetrical trigonal planar shape is 120°. Therefore, each C-C-H or C-C=C bond angle equals 120° in benzene (C6H6).
An astonishing fact is that each carbon-carbon bond length is equivalent and equal to 139 pm in benzene as opposed to a shorter C=C bond and longer C-C bond length, as expected. This fact further endorses that benzene is a resonance-stabilized molecule.
In contrast, each C-H bond length equals 109 pm in benzene.
Is Benzene (C6H6) polar or nonpolar?
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 and C=C bonds present in benzene 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 benzene.
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 atom attracts the C-H electron cloud to a minutely greater extent. Oppositely charged dipoles develop in the benzene molecule.
However, it is due to the symmetrical hexagonal molecular arrangement that the charged electron cloud stays uniformly distributed overall in benzene.
Moreover, the intermolecular forces of hydrogen pull equally in all directions. All forces cancel out, and there is no net force in one particular direction.
The individual C-H dipole moments get canceled, making benzene (C6H6) a non-polar molecule overall (net µ = 0).
What is the Lewis dot structure for benzene (C6H6)?
The Lewis dot structure for benzene (C6H6) displays a total of 30 valence electrons i.e., 30/2 = 15 electron pairs.
It comprises 6 C-atoms and 6 H-atoms.
The six C-atoms are arranged as a hexagonal ring containing 3 C-C single and 3 C=C double covalent bonds at alternate positions.
Each C-atom is bonded to an H-atom outside the hexagon.
There is no lone pair of electrons on either of the carbon or hydrogen atoms in the C6H6 Lewis structure.
How many bond pairs and lone pairs of electrons are present in the benzene Lewis structure?
In the Lewis structure of benzene (C6H6), there are 15 bond pairs and no lone pairs of electrons.
The 15 bond pairs include 3 C-C, 3 C=C and 6 C-H bonded electrons.
How many resonance structures are possible for representing the benzene molecule?
The following 5 resonance structures can be used to represent benzene (C6H6).
The actual benzene molecule is a weighted average of the above resonance structures. It is known as the resonance hybrid. The Kekule structures have maximum contribution in the resonance hybrid, while the Dewar structures contribute minimally.
What is the shape of C6H6?
The benzene (C6H6) molecule is made up of 6 C-atoms arranged symmetrically in a hexagonal ring arrangement. The shape of C6H6 w.r.t each C-atom in the hexagon is trigonal planar.
How is the shape of cyclohexane (C6H12) different from that of benzene (C6H6)?
In cyclohexane (C6H12), each C-atom is covalently bonded to 2 C-atoms and 2 H-atoms. Thus, its shape is tetrahedral w.r.t each C-atom.
Contrarily, the shape of benzene (C6H6) w.r.t each C-atom is trigonal planar.
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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