CH3OH is the chemical formula of methanol, and it is the simplest alcohol. It has a faintly sweet, pungent smell, and its molar mass is 32.04 g/mol.
In chemistry, it is used as an ingredient to make a variety of chemicals. It is also used to remove water from automotive and aviation fuels.
To find out whether the methanol CH3OH molecule is polar or non-polar, continue reading the article.
Is CH3OH polar or non-polar?
Methanol (CH3OH) is a polar molecule. It consists of one carbon (C) atom, three hydrogens (H) atoms, and a hydroxyl (OH) functional group. The carbon is kept at the central position, and all 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. In comparison, an electronegativity difference of 0.89 units exists between the carbon and oxygen atoms in the C-O bond, while an even higher electronegativity difference of 1.24 units exists between oxygen and hydrogen atoms in the O-H bond in CH3OH.
In this way, all three C-H bonds and each of the C-O and O-H bonds are individually polar in the CH3OH molecule.
However, in CH3OH, the highly electronegative oxygen atom not only attracts the shared electron cloud of the C-O bond but also attracts C-H and O-H bonded electrons. The electron cloud does not stay uniformly distributed in the molecule overall. As a result, the CH3OH molecule is overall polar (net µ =1.69 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 methanol (CH3OH) is overall a polar molecule.
Factors affecting the polarity of CH3OH
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 Hydrogen is 1s1. According to this electronic configuration, an H-atom has 1 electron only in its valence shell. It thus needs 1 more electron to complete its duplet.
Conversely, oxygen (O) is present in group VI A of the Periodic Table. The electronic configuration of an oxygen atom is 1s2 2s2 2p4. As per this electronic configuration, an O-atom has a total of 6 valence electrons. It is thus short of 2 valence electrons that are required so that an O-atom can achieve a complete octet electronic configuration.
Hence, in CH3OH, the central C-atom is single-bonded to three H-atoms and one O-atom of the OH functional group via single covalent bonds.
The structure contains three C-H, one C-O, and one O-H bond overall. In this way, all bonded atoms attain a stable electronic configuration via chemical bonding in CH3OH.
All the valence electrons of the central carbon atom get consumed in the bond formation. Thus, there is no lone pair of electrons on the central C-atom in CH3OH. However, there are 2 lone pairs of electrons on the O-atom in CH3OH.
Atom
Electronic configuration
Valence electrons
Carbon (6C)
1s2 2s2 2p2
4
Hydrogen (1H)
1s1
1
Oxygen (8O)
1s2 2s2 2p4
6
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.
Contrarily, the electronegativity difference between C-atom (E. N= 2.55) and O-atom (E. N= 3.44) in the C-O bond is 0.89units and is an extremely polar bond.
Similarly, the electronegativity difference is even higher between O-atom (E. N= 3.44) and H-atom (E. N= 2.20) in the O-H bond, i.e., 1.24units.
Thus all the covalent bonds present in the CH3OH molecule are individually polar. Consequently, charged poles develop in the molecule. The oxygen atom present in the CH3OH molecule gains a partial negative charge (Oδ-), while the central C-atom (Cδ+) and the hydrogen atoms (Hδ++) obtain partial positive charges.
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 highly polar bonds of CH3OH, the dipole moment of polar C-O bond points from Cδ+ to Oδ- while the dipole moment of polar O-H bond points from Hδ+ to Oδ-. The dipole moments of the weakly polar C-H bonds point from Hδ++ to Cδ+ (as shown below).
Molecular geometry
As discussed already, the CH3OH molecule consists of a C-atom at the center while O and H atoms occupy terminal positions.
There are a total of 14 valence electrons in the CH3OH Lewis structure, including 5 bond pairs and 2 lone pairs. Both the lone pairs are present on the O-atom, while there is no lone pair of electrons on the central C-atom or any of the H-atoms, respectively.
The CH3OH molecule can adopt two different shapes as per the valence shell electron pair repulsion (VSEPR) theory of chemical bonding.
Considering the carbon (C) atom as the central atom, CH3OH is an AX4-type molecule. It is bonded to four different atoms, and there is no lone pair of electrons present on it. Thus it adopts a tetrahedral shape and molecular geometry.
Contrarily, if we consider O-atom as the central atom in CH3OH, it is an AX2E2-type molecule, as the oxygen atom contains 2 lone pairs of electrons. Lone pair-lone pair and lone pair-bond pair repulsions distort the shape and geometry of the molecule and lead to an asymmetric bent shape.
In either case, the dipole moments of individually polar bonds do not get canceled in the molecule overall.
The highly electronegative O-atom not only attracts the shared electron cloud of the C-O bond but also attracts the C-H and O-H bonded electrons. The electron cloud stays non-uniformly distributed in the molecule overall. Consequently, methanol (CH3OH) is overall a polar molecule (net µ = 1.69 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
A specific electronegativity difference exists between the bonded atoms in each of the C-H, C-O, and O-H bonds in the CH3OH molecule.
The polar bonds possess a dipole moment.
The highly electronegative O-atom attracts the shared electron cloud from all the electron pairs. The C-H, C-O, and O-H dipole moments do not get canceled.
Thus, CH3OH is overall a polar molecule with a net dipole moment of µ = 1.69 D.
Which of the two, CH3CH2OH and CH3OH, is more polar?
Both ethanol (CH3CH2OH) and methanol (CH3OH) are polar alcohol molecules.
The molecules contain polar C-H, C-O and O-H bonds with definite dipole moment values. Both the molecules possess a regular tetrahedral shape w.r.t the C-atom while an asymmetric bent or V-shape w.r.t O-atom.
The highly electronegative oxygen atom attracts the shared electron cloud from each bond strongly towards itself, leading to an overall molecular polarity.
CH3OH is more polar as compared to CH3CH2OH because of a shorter alkyl chain. The length of its alkyl chain is inversely related to an organic molecule’s polarity.
Which is more polar, CH3OH or H2O?
Water (H2O) is definitely more polar (net µ = 1.85 D) than CH3OH (net µ = 1.69 D).
Both the molecules possess a bent or V-shape w.r.t central oxygen atom. The shared electron cloud stays non-uniformly spread over the molecule.
Both the O-H bonds are highly polar in H2O, with an electronegativity difference of 1.24 units between the oxygen and hydrogen atoms.
While in CH3OH, three weakly polar C-H bonds are also present that decrease the net dipole moment.
Which is the most polar molecule: CH3Cl, CH3NH2, CH3OH, or CH3SH?
Chloromethane (CH3Cl) has a tetrahedral shape. The highly electronegative Cl-atom attracts C-H electrons in addition to attracting the C-Cl bonded electron pair. The electron cloud stays non-uniformly distributed; thus, it is polar with net µ = 1.86 D.
All atoms in the CH3OH molecule, including carbon, hydrogen, and oxygen, obtain a formal charge equal to zero; hence overall charge present on the methanol molecule is Zero.
Summary
Methanol (CH3OH) is a polar molecule.
It consists of three C-H, one O-H, and one C-O bond.
C-H bonds are weakly polar with an electronegativity difference of 0.35 units. While C-O and O-H bonds are highly polar with an electronegativity difference of 0.89 and 1.24 units, respectively.
Methanol CH3OH has a tetrahedral molecular geometry w.r.t carbon atom while it has a bent, angular, or V-shape w.r.t oxygen atom.
∠H-C-H is 109.5° and ∠ C-O-H is 104.5°.
The highly electronegative O-atom attracts the shared electron cloud from each of the C-H bonds in addition to attracting C-O and O-H bonded electrons.
The dipole moments of individually polar C-H, C-O, and O-H bonds do not get canceled in the molecule overall. Thus, methanol (CH3OH) is a polar molecule overall with net µ = 1.69 D.
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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