Is Benzene (C6H6) polar or nonpolar? - Polarity of C6H6
C6H6 is the chemical formula of the widely popular benzene. It is a colorless aromatic hydrocarbon with a sweet odor, but overexposure to this chemical substance can cause neurological disorders. Benzene has a molar mass of 78.11 g/mol.
Interestingly, natural sources of benzene (C6H6) include volcanoes and forest fires.
Are you curious to know whether this highly flammable molecule, C6H6, is polar or non-polar? To find that out, continue reading the article.
Is Benzene (C6H6) polar or non-polar?
Benzene (C6H6) is a non-polar molecule. It consists of six carbon (C) atoms and six hydrogens (H) atoms. The carbon atoms are arranged in a hexagonal (six-cornered) ring arrangement, making three C=C double bonds and three C-C single covalent bonds alternately. Each hydrogen atom is bonded to a single C-atom in order to complete its valency.
In C6H6, three different types of bonds (C-C, C=C, and C-H) are present. An electronegativity difference of 0.35 units exists between the bonded atoms in the C-H bond, making it weakly polar. Each C-H bond thus possesses a small dipole moment value (symbol µ).
However, there is no electronegativity difference between the identical carbon atoms in a C-C or C=C bond. Consequently, all the C-C and C=C bonds are non-polar in C6H6 and do not possess any dipole moment value.
However, it is due to the symmetrical shape of the C6H6 molecule that the individual C-H dipole moments are directed in opposite directions and thus get canceled uniformly.
The charged electron cloud does not stay uniformly distributed in the molecule overall. As result, the Benzene (C6H6) molecule is overall non-polar (net µ =0).
A molecule is polar if there is a non-uniform charge distribution present in it.
If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that benzene (C6H6) is overall a non-polar molecule.
Factors affecting the polarity of C6H6
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Carbon (C) is present in Group IV A (or 14) of the Periodic Table. The electronic configuration of a carbon atom is 1s2 2s2 2p2. As per this electronic configuration, a C-atom has a total of 4 valence electrons. It is thus short of 4 more electrons that are required so that the carbon atom can achieve a complete octet electronic configuration.
Hydrogen (H) is present in Group IA (or 1) of the Periodic Table. The electronic configuration of hydrogen is 1s1. According to this electronic configuration, each H-atom has only a single valence electron in its only shell. It thus lacks 1 more electron to complete its outer electron shell.
The Lewis dot structure of C6H6 displays three C-C, three C=C, and six C-H bonds. Each C-atom obtains a complete octet electronic configuration, while each H-atom obtains a complete duplet via chemical bonding in C6H6.
All 4 valence electrons of all the C-atoms used in covalent bonding denote there is no lone pair on any one C-atom; thus, there is no distortion present in the shape and geometry of the molecule.
Conversely, the structure is resonance stabilized, which means that in addition to the structure shown above, there are the following other possibilities for drawing the C6H6 Lewis structure.
The actual benzene structure is a hybrid of all the contributing resonance forms; the delocalized electrons are shown as a ring within the hexagonal arrangement, as shown below.
Atom
Electronic configuration
Valence electrons
Carbon (6C)
1s22s22p2
4
Hydrogen (1H)
1s1
1
In C6H6, the central hexagonal ring is completely non-polar due to identical carbon atoms present in it with zero electronegativity differences.
However, each C-H bond is only slightly polar. Carbon (E.N = 2.55) and hydrogen (E.N = 2.20) possess an electronegativity difference of 0.35 units and, thus, a small dipole moment value.
Each C-atom gains a partial negative charge (δ–) while each H-atom gains a partial positive charge (δ+), as shown below.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.
So the dipole moment of each C-H bond should ideally point from Hδ+ to Cδ-. But the C-H dipole moments in benzene are an exception.
C6H6 is resonance stabilized.
As the charged electron cloud of hexagonally arranged C-atoms gets involved in resonance present within the ring, therefore, an overall electron deficiency develops near the C-atoms.
Each C-atom is only slightly more electronegative than the H-atoms to overcome this deficiency. Thus the center of gravity of C6H6 becomes a center of positive charge as well.
In short, in the weakly polar bonds of C6H6, the dipole moment of each C-H bond points outwards, from C to H (as shown below).
Molecular geometry
Benzene is a symmetrical hexagonally arranged molecule. According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, it is an AX3E0-type molecule w.r.t each C-atom.
To one C-atom at the center (A), three bonded atoms (X) are attached (2 neighboring C-atoms and 1 H-atom), and the central C-atom does not contain any lone pair of electrons (E).
So in C6H6, the molecular geometry or shape w.r.t each C-atom is trigonal planar, due to which the bonded atoms possess mutual bond angles ∠ (C-C=C) and ∠ (C-C-H) = 120°.
It is due to the overall symmetrical hexagonal molecular shape of benzene (C6H6) that the charged electron cloud stays uniformly distributed in the molecule.
Moreover, the intermolecular forces of hydrogen pull equally in all directions. All the forces cancel out each other, and there is no net force in one particular direction.
Hence, the individual C-H dipole moments of the benzene C6H6 molecule cancel out each other, making it non-polar overall (net µ = 0).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), nitrous oxide (N2O), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), ethane (C2H6), propane (C3H8), ethyne (C2H2), benzene (C6H6), cyclohexane (C6H12), etc.
C6H6 is a symmetrical and planar molecule having a ring-like structure. It contains six slightly polar C-H bonds with an electronegativity difference of 0.35 units between the bonded atoms. Six non-polar C-C and C=C bonds are also present in the benzene ring.
It is due to the symmetrical hexagonal ring structure of benzene that opposite and equal dipoles cancel out each other. As a result, the net dipole moment of benzene is zero.
Thus, Benzene (C6H6) is overall a non-polar molecule with the net dipole moment of µ = 0.
How do dipole moments in benzene affect the polarity of the molecule?
The benzene molecule consists of 6 pairs of carbon and hydrogen atoms, with each C-atom connected in a ring-like structure.
The C-H bond results in a little dipole moment due to the difference in the electronegativity of the bonded atoms.
Still, all the dipoles are in such a direction that they cancel out each other. As a result, the benzene molecule is overall non-polar (net µ = 0).
Why does benzene get dissolved in polar solvents?
Substances with no permanent dipole moment are non-polar such as toluene (C6H5CH3), octane (C8H18), benzene (C6H6), etc.
Contrarily, polar substances possess specific dipole moment values, such as ethanol (CH3CH2OH), methanol (CH3OH), water (H2O), etc.
Like dissolves like. Since polar and non-polar substances tend to be immiscible and (unless they react) will usually separate into layers when mixed hence benzene does not dissolve in polar substances.
Which of the two is polar, C6H6 or C6H12?
Both benzene (C6H6) and cyclohexane (C6H12) are non-polar molecules.
C6H6 consists of three types of bonds: C-C, C=C, and C-H. Each of the C-C and C=C bonds is non-polar as these are made up of identical atoms having zero electronegativity differences.
Each C-H bond is very weakly polar with a small dipole moment value. The C-H dipole moments get canceled uniformly in opposite directions in the hexagonal shape of the molecule, thus, Benzene (C6H6) is overall non-polar (net µ = 0).
C6H12 consists of two types of bonds: C-C and C-H. Each C-C bond is non-polar, while the dipole moments of very weakly polar C-H bonds get canceled equally in opposite directions, so the molecule is overall non-polar (net µ = 0).
Which of the following organic molecules is/are polar?
a) CH4 b) CH3CH2OH c) CH3OCH3 d) C6H6
Ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3) are polar molecules, while both methane (CH4) and benzene (C6H6) are non-polar.
The polarity of a molecule depends on the shape of the molecule and the electronegativity difference between bonded atoms.
CH4 consists of four slightly polar C-H bonds with very small dipole moment values. The C-H dipole moments get canceled uniformly in the symmetrical tetrahedral shape of the CH4 molecule. So it is overall non-polar (net µ = 0).
CH3CH2OH consists of weakly polar C-H bonds and a strongly polar O-H bond. The molecule possesses an asymmetrical bent or V-shape w.r.t O-atom.
Oxygen being highly electronegative attracts the C-H bonded electrons in addition to attracting the O-H electron cloud. The individual dipole moments do not get canceled overall. Thus CH3CH2OH is overall polar (net µ > 0).
CH3OCH3 consists of six weakly polar C-H bonds and two strongly polar C-O bonds, having an electronegativity difference of 0.89 units between the bonded atoms.
C6H6is a non-polar molecule as oppositely pointing small C-H dipole moments get canceled equally in the symmetrical hexagonal shape of the molecule (net µ = 0).
What are the formal charges present on the bonded atoms in C6H6?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For each C-atom
Valence electrons = 4
Bonding electrons = 1 double bond + 2 single bonds = 4 +2(2) = 8
Non-bonding electrons = 0
∴ Formal charge on each C-atom in the ring = 4 – 0 – 8/2 = 4 – 0 – 4 = 4 – 4= 0
Zero formal charges are present on each of the C and H-atoms in the C6H6 structure.
Thus, there are no or zero overall formal charges present on the benzene molecule.
Summary
Benzene (C6H6) is a non-polar molecule.
It consists of three C=C, three C-C, and six C-H bonds in the form of a symmetrical hexagonal ring.
C-H bonds are weakly polar with an electronegativity difference of 0.35 units between the bonded C-atom (E.N =2.55) and H-atom (E.N = 2.20). While all C-C and C=C bonds are purely non-polar owing to zero electronegativity differences between the identical carbon atoms.
C6H6 is resonance stabilized.
C6H6 has a trigonal planar molecular geometry w.r.t each C-atom, and thus, the bonded atoms possess a mutual bond angle of 120°.
Due to the absence of any lone pair of electrons on any one central C-atom, there is no distortion present in the shape and geometry of the molecule.
The very small C-H dipole moments get canceled equally in opposite directions. The charged electron cloud stays uniformly spread over the molecule.
The net dipole moment in C6H6 is thus µ = 0, so benzene is overall a non-polar molecule.
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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