CH3Cl is the chemical formula for the organic compound chloromethane, also known as methyl chloride. It is a clear, colorless gas and has a faintly sweet odor. CH3Cl has a molar mass of 50.49 g/mol and is used as an extractant for oil and resins, a propellant in foam production, etc. It is also used as a solvent in rubber production and in petroleum refining.
To find out whether the chloromethane CH3Cl molecule is polar or non-polar, continue reading the article.
Is CH3Cl polar or non-polar?
Chloromethane (CH3Cl) is a polar molecule. CH3Cl consists of one carbon (C) atom, three hydrogens (H) atoms, and one chlorine (Cl) atom. The carbon is kept at the central position, and other atoms are at the surrounding positions, making a tetrahedral molecular shape.
An electronegativity difference of 0.35 units exists between C-H bonds, making them weakly polar, while an electronegativity difference of 0.61 units exists between a carbon and a chlorine atom in the C-Cl bond in CH3Cl. Thus, the C-Cl bond is strongly polar in the CH3Cl molecules and possesses a high dipole moment value (symbol µ).
In the CH3Cl, the highly electronegative chlorine atom not only attracts the shared electron cloud of the C-Cl bond but also the C-H bonded electrons. The electron cloud does not stay uniformly distributed in the molecule overall. As a result, the CH3Cl molecule is overall polar (net µ =1.86 D).
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 chloromethane CH3Cl is overall a polar molecule.
Factors affecting the polarity of CH3Cl
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 of the Periodic Table. The electronic configuration of carbon 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 of the Periodic Table. The electronic configuration of a hydrogen atom is 1s1. According to this electronic configuration, an H-atom has 1 electron in its only shell and lacks one more electron to complete its duplet.
Conversely, Chlorine (Cl) is present in Group VII A of the Periodic Table. The electronic configuration of chlorine is 1s2 2s2 2p6 3s2 3p5, which translates as a Cl-atom having a total of 7 valence electrons. It thus has a deficiency of one electron to complete its stable octet configuration.
Hence, in CH3Cl, the central C-atom is bonded to three H-atoms and one Cl-atom via four single covalent bonds. The structure contains three C-H bonds and one C-Cl bond in its tetrahedral molecular geometry.
In this way, all bonded atoms attain a completely stable electronic configuration via chemical bonding in CH3Cl.
All the valence electrons of carbon get consumed in the bond formation. There is no lone pair of electrons on the central C-atom in CH3Cl. Hence, there is no distortion in the shape or geometry of the molecule.
Atom
Electronic configuration
Valence electrons
Carbon (6C)
1s2 2s2 2p2
4
Hydrogen (1H)
1s1
1
Chlorine (17Cl)
1s2 2s2 2p6 3s2 3p5
7
The electronegativity difference between C-atom (E. N= 2.55) and H-atoms (E. N= 2.20) in each of the three C-H bonds is 0.35 units. Due to this small electronegativity difference, C-H bonds are considered weakly polar in CH3Cl.
Contrarily, the more electronegative Cl-atom (E. N= 3.16) strongly attracts the shared electron cloud away from the central C-atom (E. N= 2.55) in the C-Cl bond present in CH3Cl.
Thus, the chlorine atom present in the CH3Cl molecule gains a partial negative (Clδ-) charge, while central carbon obtains a partial positive (Cδ+) charge.
As a result, with an electronegativity difference of 0.61 units in the C-Cl bond is strongly polar in CH3Cl. The Cl-atom attracts C-H bonded electrons as well in addition to attracting the C-Cl electron pair. Thus, the H-atoms also acquire partial positive (Hδ++) charges as shown below.
Dipole Moment
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge. So in CH3Cl, the dipole moment of polar C-Cl bond points from Cδ+ to Clδ-(as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, CH3Cl is an AX4-type molecule. To one C-atom at the center (A), four bonded atoms (X) are attached (three H-atoms and one Cl-atom), and the central C-atom contains no lone pair (E).
So, the molecular geometry or shape of CH3Cl is identical to its ideal electron pair geometry, i.e., tetrahedral. To minimize the repulsions and to attain stability in the tetrahedral structure, the bonded atoms of the CH3Cl molecule possess a mutual bond angle of 109.5°.
Although, due to the absence of any lone pair of electrons on the central C-atom, the CH3Cl molecule has an identical molecular and electron geometry that is tetrahedral; still the highly electronegative Cl-atom not only attracts the shared electron cloud of the C-Cl bond but also attracts C-H bonded electrons.
The electron cloud stays non-uniformly distributed in the molecule overall. Consequently, CH3Cl is overall a polar molecule (net µ = 1.86 D).
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), methyl chloride (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.
CH3Cl molecule has one C-Cl and three C-H bonds. C-H bonds have weak polarity due to a small electronegativity difference (0.35 units) between the bonded atoms. While in the C-Cl bond, Cl-atom is more electronegative (E. N= 3.16) than C-atom (E. N= 2.55). So the C-Cl is strongly polar.
CH3Cl has tetrahedral geometry; still, the highly electronegative Cl-atom not only attracts the shared electron cloud of the C-Cl bond but also attracts the C-H electrons.
The electron cloud stays non-uniformly distributed in the molecule overall. In conclusion, CH3Cl is a polar molecule having a net dipole moment of 1.86 Debye.
Thus, CH3Cl is overall a polar molecule with a net dipole moment of µ = 1.86 D.
Which is more polar out of CH3Cl, CH2Cl2, and CHCl3?
The polarity of the CHX-type molecule decreases as the number of halogens (X) attached increases.
In CH3Cl, there are three C-H bonds and one C-Cl bond. It is strongly polar because the small net dipole moment of three C-H bonds does not get canceled with the high dipole moment of a strongly polar C-Cl bond.
The charged electron cloud stays non-uniformly distributed, strongly attracted towards the single Cl-atom. Thus CH3Cl is extremely polar (net µ = 1.86 D).
CH2Cl2 has two C-H bonds and two C-Cl bonds. The dipole moments of two C-H bonds cancel out the dipole moments of two C-Cl bonds to a small extent, so net µ = 1.67 D for CH2Cl2.
In CHCl3, there are three C-Cl bonds and only one C-H bond. The dipole moments get canceled to a larger extent, thus net µ = 1.08 D for CHCl3.
The polarity increases in the order: of CHCl3 < CH2Cl2 < CH3Cl.
Why is CH3Cl polar while CCl4 is a non-polar molecule?
Both CH3Cl and CCl4 molecules possess a tetrahedral shape and electron geometry.
In CH3Cl, there are three weakly polar C-H bonds and one strongly polar C-Cl bond. The dipole moments of individually polar bonds do not get canceled equally on each side of the molecule; thus, it is overall a polar molecule (net µ > 0).
Contrarily, the CCl4 molecule consists of four identical C-Cl bonds. The net dipole moment of three downwards-pointing C-Cl bonds gets canceled with the dipole moment of an upwards-pointing C-Cl bond.
The charged electron cloud stays uniformly distributed over the molecule. Thus it is overall non-polar (net µ = 0).
What are the formal charges present on the bonded atoms in CH3Cl?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
All atoms in the CH3Cl molecule, including carbon, hydrogen, and chlorine, obtain a formal charge equal to zero; hence no overall charge is present on the chloromethane molecule.
Summary
Chloromethane (CH3Cl) is a polar molecule.
It consists of three weakly polar C-H bonds with an electronegativity difference of 0.35 units and one strongly polar C-Cl bond due to an electronegativity difference of 0.61 units.
Chloromethane (CH3Cl) has a tetrahedral molecular shape with bond angles of 109.5°.
Due to the absence of any lone pair of electrons on the central C-atom, the CH3Cl molecule has a symmetrical tetrahedral shape.
In CH3Cl, there is a permanent dipole moment of 1.86 Debye in the molecule.
The net dipole moment in CH3Cl is 1.86 Debye, so it is overall a polar molecule.
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