Is Toluene (C7H8) polar or nonpolar? – Polarity of Toluene
Toluene, also known as toluol is represented by the chemical formula C7H8. It is a substituted aromatic hydrocarbon (molar mass = 92.14 g/mol).
The structural formula for toluene includes a methyl (CH3) group present on a phenyl (C6H5) ring. Therefore, the IUPAC name for toluene is methylbenzene.
It exists as an easily vaporizable, colorless liquid at r.t.p. Toluene is most commonly used as a solvent in the chemistry laboratory.
If you are interested to know whether toluene is polar or non-polar? Then let’s find out!
Is toluene polar or non-polar?
Toluene, or methylbenzene (C7H8), is a non-polar chemical compound. It is a hydrocarbon containing only two elements i.e., carbon (C) and hydrogen (H).
The phenyl (C6H5) ring consists of purely non-polar C-C single and C=C double covalent bonds. The C-H bonds are slightly polar as per an electronegativity difference of only 0.35 units between a carbon and a hydrogen atom.
However, the small C-H dipole moments get canceled equally due to the symmetrical trigonal planar or tetrahedral shape of toluene w.r.t each C-atom and a symmetrical hexagonal arrangement of C-atoms within the phenyl ring.
This results in a non-polar molecule overall (net µ = 0).
Name of molecule
Toluene (C7H8)
Bond type
Non-polar covalent (C-C and C=C)
Very weakly polar covalent (C-H)
Molecular geometry
Trigonal planar (w.r.t each C-atom in phenyl ring)
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 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 toluene is overall non-polar.
Factors affecting the polarity of toluene
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Carbon (C) belongs to Group IV A (or 14) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p2. It has a total of 4 valence electrons which means it is deficient in 4 more electrons in order to gain a stable octet electronic configuration.
Hydrogen (H) lies at the top of the Periodic Table in Group I A (or 1). Its electronic configuration is 1s1, which implies it lacks 1 more electron to complete its duplet.
A toluene (C7H8) molecule comprises a total of 4 C-C single covalent bonds, 3 C=C double bonds, and 8 C-H bonds.
In this way, each C-atom attains a complete octet electronic configuration while all the H-atoms complete their duplets.
All 4 valence electrons of each C-atom get consumed in covalent bonding in C7H8. So, there is no lone pair of electrons on any one C-atom; thus, no distortion is witnessed in its shape and/or geometry, as shown in the Lewis dot structure drawn below.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Carbon (6C)
1s2 2s2 2p2
4
Zero or no electronegativity difference exists between identical carbon atoms in a C-C or C=C bond. Therefore, all carbon-carbon bonds are purely non-polar in the phenyl ring in toluene.
In contrast, an electronegativity difference of 0.35 units exists between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom in each C-H bond.
It is less than that required for a covalent chemical bond to be polar as per Pauling’s electronegativity scale i.e., 0.4 units.
Still, each C-H bonded C-atom gains a partial negative (δ–) charge while the corresponding H-atom obtains a partial positive (δ+) charge, considering the fact that it is formed between two dissimilar atoms, which may lead to a slight distortion in electron cloud distribution.
As a result, each C-H bond of toluene is considered very weakly polar, individually.
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 charge 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, in toluene, C-C or C=C bonds have no dipole moments, while the small dipole moment of each C-H bond points from Hδ+ to Cδ-, as shown below.
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, toluene is an AX3-type molecule w.r.t each C-atom in the phenyl ring and an AX4-type molecule w.r.t C-atom in the CH3 group.
In the phenyl ring, to a carbon atom at the center (A), three bond pairs (X) are attached i.e., 2 other C-atoms and an H-atom, and it has no lone pairs of electrons (E). Therefore, the molecular shape of toluene is trigonal planar w.r.t each C-atom in the phenyl ring.
To the C-atom of the methyl group, four bond pairs i.e., 1 C-atom and 3 H-atoms are attached, and it has no lone pairs. Hence, the shape is tetrahedral w.r.t C-atom belonging to the methyl group.
The absence of any lone pairs of electrons in C7H8 ensures there are no lone pair-lone pairs or lone pair-bond pair electronic repulsions to distort the shape and geometry of the molecule.
The small C-H dipole moments get canceled uniformly to yield an overall non-polar toluene molecule (net µ = 0).
The bonded atoms occupy a symmetrical, hexagonal arrangement within the ring, which further endorses the non-polarity effect as the charged electron cloud stays uniformly distributed overall.
FAQ
Is toluene polar or not?
No. Toluene is not polar; rather, it is a non-polar chemical compound.
Toluene (C7H8) is an aromatic hydrocarbon containing C-C, C=C and C-H bonds.
All C-C and C=C bonds are purely non-polar as they consist of two identical carbon atoms having zero or no electronegativity differences.
A C-H bond is very weakly polar, having an electronegativity difference of 0.35 units between the single-bonded carbon and hydrogen atoms.
The small C-H dipole moments get canceled equally to yield an overall non-polar molecule (net µ = 0).
Which one is more polar, benzene or toluene?
Both benzene (C6H6) and toluene (C7H8) are non-polar aromatic hydrocarbons.
Both C6H6 and C7H8 consist of C-C, C=C, and C-H covalent bonds.
The carbon-carbon bonds in the symmetrical hexagonally arranged benzene ring are purely non-polar.
The C-H bonds are very weakly polar with small dipole moment values.
However, it is due to the symmetrical arrangement of the bonded atoms in both benzene and toluene that the charged electron cloud stays uniformly distributed to yield an overall non-polar molecule.
Why is toluene a non-polar solvent while chloroform is a polar solvent?
Toluene (C7H8) is non-polar as it consists of non-polar carbon-carbon and weakly polar carbon-hydrogen bonds. Due to small or negligible electronegativity differences between the bonded atoms, the molecule stays non-polar overall.
Contrarily, chloroform (CHCl3) is polar as it comprises three highly electronegative Cl-atoms. An electronegativity difference of 0.61 units is present between a carbon (E.N = 2.55) and a chlorine (E.N = 3.16) atom.
The strong C-Cl dipole moments do not get canceled with the small C-H dipole moment. Thus, chloroform is overall polar. It is used as a polar extraction solvent in the chemistry laboratory.
Is there a formal charge present on the toluene molecule?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
Zero formal charges are present on all the C and H-atoms in the C7H8 molecule. Thus, there is no or zero overall formal charge on toluene.
Summary
Toluene (C7H8 or C6H5CH3) is non-polar.
C7H8 consists of three main types of covalent bonds i.e., C-C, C=C, and C-H.
C-C or C=C bonds are non-polar as zero, or no electronegativity difference is present between identical carbon atoms.
C-H bonds are weakly polar (almost non-polar as per Pauling’s electronegativity scale) due to an electronegativity difference of 0.35 units between the bonded atoms.
The small C-H dipole moments get canceled uniformly in the symmetrical hexagonal C6H5 ring, and due to the tetrahedral shape w.r.t carbon in the CH3 group of toluene.
The charged electron cloud stays uniformly distributed. So, toluene is overall non-polar (net µ = 0).
It is thus used as a solvent for dissolving non-polar chemical compounds.
References
‘Compound Summary; Toluene.’’ Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/Toluene.
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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