Is CHCl3 polar or nonpolar? - Polarity of CHCl3

The IUPAC name for CHCl₃ is trichloromethane however you must have heard about it by its commonly used commercial name i.e., chloroform. Chloroform is a colorless, dense liquid with a very strong smell.

The IUPAC name for chloroform suggests that it is made up of three chlorine atoms bonded to a carbon atom at the center. Chloroform is formed when the 3 hydrogen atoms of methane (CH₄) get replaced by three halogen (Cl) atoms thus the name trichloromethane.

If you have any doubt about the polarity of CHCl₃ then this article is exactly what you are looking for, that is: Is CHCl₃ polar or non-polar?

 Is CHCl₃ polar or non-polar?

Chloroform (CHCl₃) is a polar molecule. Chlorine (Cl) is a highly electronegative element. It attracts the shared electron cloud of each of the three C-Cl bonds as well as the C-H bond. Oppositely charged poles develop in the molecule.

CHCl₃ has an apparently symmetric tetrahedral shape or geometry. However, dipole moments of individually polar C-Cl bonds do not get canceled even in this tetrahedral shape.

There is an overall unbalanced electron cloud density in the molecule thus CHCl₃ is a polar molecule with a net µ > 0.

Name of molecule	Trichloromethane or chloroform  (CHCl3)
Bond type	Polar covalent
Molecular geometry	Tetrahedral
Polar or Non-polar?	Polar molecule
Dipole moment	1.08 D
Bond angle	109.5º

Polar versus non-polar molecules

Different factors control the polarity of covalently bonded molecules. Three of these most important factors are:

• Electronegativity
• Dipole moment
• Molecular geometry or shape

Based on all these factors, a molecule is polar if it has an overall non-uniform electron cloud density. On the other hand, molecules are non-polar if they have a balanced net charge distribution.

This happens when the dipole moments of individually polar bonds get canceled in opposite directions due to the symmetrical shape of the molecule.

Now let’s see how all the above-mentioned factors make CHCl₃ a polar molecule with a non-uniform electron cloud distribution overall.

Factors affecting the polarity of CHCl₃

Electronegativity

Electronegativity is defined as the ability of an atom to attract a shared pair of electrons from a covalent bond.

According to the Pauling scale, a covalent bond is polar if the bonded atoms have an electronegativity difference between 0.5 to 1.6 units.

No covalent bond is purely non-polar unless it is made up of two identical atoms such as an oxygen (O₂) molecule or hydrogen (H₂) molecule.

Therefore, although there is a small electronegativity difference between a C (E.N = 2.55) and an H (E.N= 2.20) atom, electronegativity difference = 0.35 < 0.5, but still a C-H bond in CHCl₃ is slightly polar. 

Atom	Electronic configuration	Valence electrons
Carbon (6C)	1s2 2s2 2p2	4
Hydrogen (1H)	1s1	1
Chlorine (17Cl)	1s2 2s2 2p63s23p5	7

Halogens present in group VII A (or group 17) of the Periodic Table are highly electronegative elements. The halogens are short of a single electron only to complete their octet electronic configuration, so they strongly attract the shared electron cloud from a covalent bond.

Chlorine is a halogen with a high electronegativity (E.N = 3.16). There is a high electronegativity difference between a C and a Cl atom i.e., 3.16 – 2.55= 0.61 > 0.5, thus each C-Cl bond in the CHCl₃ molecule is polar.

The three Cl atoms not only attract the shared electron cloud of each C-Cl bond but also that of the C-H bond. These electronegativity differences generate oppositely charged positive (Cδ+) and negative (Clδ-) poles in the chloroform molecule.

Dipole moment

Dipole moment (µ) is a vector quantity defined as the product of electrical charge (Q) and charge separation (r).

The charge separation is measured from the center of the positive pole to the center of the negative pole.                                                                                                            

The dipole moment of the C-Cl bond points from the partial positively charged center ( C^δ+ ) to the partial negatively charged center (Cl^δ- ).

A carbon atom is comparatively more electronegative than a hydrogen atom so the dipole moment of the C-H bond points from C^δ+ to H^δ++.

 

Molecular geometry or shape

Carbon belongs to group IV A (or group 14) of the Periodic Table. It has 4 valence electrons available for bonding. In CHCl₃, the central carbon is bonded to 1 hydrogen and 3 chlorine atoms.

In this way, the carbon, as well as all the chlorine atoms, achieve a stable octet electronic configuration while hydrogen completes its duplet.

All the valence electrons of carbon get involved in covalent bond formation in CHCl₃. So, there are 4 bond pairs (B) around the central carbon atom (A) and no lone pair.

Such a  molecule is known as an AB₄ type molecule according to the Valence Shell Electron Pair Repulsion (VSEPR) theory of chemical bonding.

The molecule (CHCl₃) has a tetrahedral geometry with a mutual bond angle of 109.5°. Although tetrahedral is technically a symmetrical shape as 4 atoms are present at the four corners of a tetrahedron.

But in this case, the downwards pointing Cl bonds attract the shared electron cloud of the C-H bond in addition to attracting the electrons from each C-Cl bond.

This leads to a disturbed/asymmetrical electron cloud over the molecule. The dipole moments of individual C-Cl bonds do not get canceled rather the polarity effect adds up to yield a polar CHCl₃ molecule. It has a net dipole moment of 1.08 D.

Also check –

• CHCl3 lewis structure, molecular geometry, bond angle, hybridization
• How to tell if a molecule is polar or nonpolar?
• Is SF4 polar or nonpolar?
• Is CO2 polar or nonpolar?
• Is NH3 polar or nonpolar?
• Is SO2 polar or nonpolar?
• Is SO3 polar or nonpolar?
• Is H2O polar or nonpolar?
• Is H2S polar or nonpolar?
• Is HCN polar or nonpolar?
• Is CCl4 polar or nonpolar?
• Is XeF4 polar or nonpolar?
• Is CH2O polar or nonpolar?
• Is BrF5 polar or nonpolar?
• Is SF6 polar or nonpolar?
• Is BF3 polar or nonpolar?
• Is PCl5 polar or nonpolar?

FAQ

Why is CHCl3 a polar molecule even though it has a tetrahedral shape?

CHCl3 is a polar molecule because the shared electron cloud is asymmetrically distributed over the tetrahedral shape of the molecule. Halogen atoms are highly electronegative, so the Cl atoms present in CHCl3 attract the shared electron cloud of not only the C-Cl bonds but also the C-H bond. Dipole moments of individually polar bonds do not get canceled in CHCl3  overall so it is a polar molecule.

If CHCl3 is polar, then why doesn’t it dissolve in water (a polar solvent)?

CHCl3 is partially miscible with water due to its polar ends but CHCl3 cannot form hydrogen bonding with H2O molecules. Thus, CHCl3 does not completely dissolve in water. For H-bonding, hydrogen atoms must be directly bonded to the electronegative atoms.

CH4 and CHCl3 are both tetrahedral molecules but CHCl3 is polar while CH4 is non-polar. Why?

Methane (CH4 ) is made up of four equivalent C-H bonds. Carbon is slightly more electronegative than hydrogen, so each C-H bond is weakly polar. But the dipole moments of these weakly polar bonds get canceled in opposite directions due to the symmetric tetrahedral shape of the CH4. Thus, CH4 is a non-polar molecule with a net µ =0. Trichloromethane (CHCl3) is formed by replacing H-atoms with three highly electronegative Cl atoms. Cl attracts the shared electron cloud from the C-H bond in addition to attracting the electrons from each C-Cl bond. Thus, CHCl3 has an asymmetric non-uniformly distributed electron cloud overall and it is polar with a net µ > 0.

Which is more polar, CH3Cl or CHCl3?

CH3Cl (µ = 1.87 D) is more polar as compared to CHCl3 (µ= 1.08 D). One Cl atom present at the apex of a tetrahedron more strongly attracts the shared electron cloud from each C-H bond as compared to three Cl atoms attracting the electron cloud from a single C-H bond. Some dipole moment cancelation occurs in the CHCl3 molecule which decreases the net dipole moment value of the molecule as opposed to the net dipole moment in the CH3Cl molecule.

Why is CHCl3 a polar molecule but considered a non-polar solvent?

CHCl3 is a polar molecule on account of the difference in the electronegativity of its bonded atoms. But it is generally considered a non-polar organic solvent in the chemistry laboratory because a large number of CHCl3 molecules together have a low dielectric constant.

Explain hybridization in CHCl3.

The central carbon atom in CHCl3 is sp3. The electronic configuration of carbon is 1s22s22p2 and the electronic configuration of chlorine is 1s22s22p63s23p5. During bond formation in CHCl3, one 2s electron of C shifts to the empty 2p orbital. The 2s and three 2p orbitals hybridize to produce four sp3 hybrid orbitals, each containing a single unpaired electron. One sp3 hybrid orbital overlaps with the s orbital of H to form a C-H sigma (σ) bond while the other three sp3 hybrid orbitals overlap with the p orbitals of Cl to form the remaining 3 sigmas (σ) bonds.

Summary

• Chloroform (CHCl₃) is a polar molecule.
• It has three Cl atoms and one H atom bonded to a C at the center.
• There is a significant electronegativity difference (0.61 units) between the bonded C and Cl atoms.
• Cl strongly attracts the shared electron cloud from each C-Cl bond.
• There is a small electronegativity difference between the bonded C and H atoms, so Cl attracts the electron cloud of the C-H bond as well.
• The electronic geometry and shape of the CHCl₃ molecule is tetrahedral with a mutual bond angle of 109.5° but the shared electron cloud of the molecule is not balanced overall.
• Thus, CHCl₃ is overall polar with a net dipole moment of 1.08 D.