Is CH3CH2OH polar or nonpolar? - Polarity of CH3CH2OH
CH3CH2OH is the chemical formula for the most widely popular ethanol, the second member of the alcohol family. Ethanol (molar mass = 46.07 g/mol) is used to prepare alcoholic beverages, in pharmaceutical preparations, perfumes, cosmetics, etc.
The question today is whether CH3CH2OH is polar or non-polar. So let’s find out!
Is CH3CH2OH polar or non-polar?
Ethanol (CH3CH2OH) is an extremely polar chemical compound.
Each CH3CH2OH molecule comprises two C-atoms, six H-atoms, and an O-atom. A small electronegativity difference (0.35 units) is present between a carbon and a hydrogen atom in each C-H bond.
However, a large electronegativity difference (1.24 units) exists between the single-covalently bonded hydrogen and oxygen atoms in a hydroxyl (OH) functional group.
Therefore, the O-H bond possesses a high dipole moment value in CH3CH2OH.
Oxygen being highly electronegative out of all the atoms available, strongly attracts the C-C and C-H bonded electrons in addition to attracting the O-H shared electron cloud.
The molecule attains an asymmetrical bent shape w.r.t the O-atom in which the C-H and O-H dipole moments do not get canceled at all; rather, the overall polarity effect is enhanced.
The charged electron cloud stays non-uniformly spread over the molecule; thus, CH3CH2OH is overall polar (net µ> 0).
Name of molecule
Ethanol (CH3CH2OH)
Bond type
Polar covalent
Molecular geometry
Tetrahedral (w.r.t C-atom), bent, angular, or V-shaped (w.r.t O-atom)
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 how ethanol (CH3CH2OH) is a polar molecule in light of the above three factors.
Factors affecting the polarity of CH3CH2OH
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 or molecular ion, the higher the bond polarity.
Hydrogen (H) lies at the top of the Periodic Table with 1 valence electron. It needs 1 more electron to complete its duplet.
Carbon (C) is present in Group IV A (or 14) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p2, which denotes there are 4 valence electrons present in a C-atom. Each C-atom thus has a deficiency of 4 more valence electrons to achieve a complete octet electronic configuration.
The electronic configuration of an oxygen (O) atom (present in Group VI A or 16) is 1s2 2s2 2p4. It possesses a total of 6 valence electrons which denotes the lack of 2 more electrons for an oxygen atom to complete its octet.
The Lewis dot structure of CH3CH2OH displays a total of 5 C-H bonds, 1 C-C bond at the center, 1 C-O bond, and a terminal O-H bond.
All C-atoms and the O-atom have a complete octet, while each H-atom has a complete duplet electronic configuration in this structure.
There are no lone pairs of electrons on any of the two C-atoms; however, the O-atom carries 2 lone pairs, respectively.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Oxygen (8O)
1s22s22p4
6
Carbon (6C)
1s22s22p2
4
A C-C bond present at the center of the CH3CH2OH molecule is purely non-polar, as it comprises two identical C-atoms with a zero electronegativity difference.
In contrast, each C-H bond is very weakly polar owing to an electronegativity difference of just 0.35 units between the bonded carbon (E.N = 2.55) and hydrogen (E.N = 2.20) atoms.
The C-O bond is polar as an electronegativity of 0.89 units exists between the bonded carbon and oxygen (E.N = 3.44) atoms.
On the other hand, the O-H bond is strongly polar, with a high electronegativity difference of 1.24 units between the concerning oxygen and hydrogen atoms.
Thus, in the CH3CH2OH molecule, the O-atom gains a partial negative (δ–) charge while the corresponding H-atom gains a partial positive charge (δ+). This implies that the O-H bond is strongly polar.
The presence of δ+ and δ++ charges on the CH3 and CH2 bonded carbon and hydrogen atoms represent an extreme electron deficiency.
Oxygen being highly electronegative, strongly attracts the electrons shared between each C-H and C-C bond as well, lending them strong partial positive charges, as shown above.
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.
In the CH3CH2OH molecule, the C-O dipole moment points from Cδ+ to Oδ– while the O-H dipole moment points from Hδ+ to Oδ-.
The small dipole moment of each C-H bond points from Hδ++ to Cδ+.
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the molecular geometry and shape of the ethanol molecule is tetrahedral w.r.t both less electronegative C-atoms, while it is bent, angular or V-shaped w.r.t the more electronegative O-atom.
The presence of 2 lone pairs of electrons on the O-atom leads to strong lone pair-lone pair and lone pair-bond pair electronic repulsions, which makes the molecule occupy a bent shape.
The O-H and C-H dipole moments do not get canceled in this asymmetrical bent shape and molecular geometry.
The charged electron cloud stays non-uniformly spread over the molecule.
CH3CH2OH is thus overall polar (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), methanol (CH3OH), dimethyl ether (CH3OCH3), ammonia (NH3), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), propane (CH3CH2CH3), sulfur trioxide (SO3), etc.
CH3CH2OH is an extremely polar molecule due to the presence of a strongly polar hydroxyl (O-H) functional group and the asymmetric bent shape of the molecule w.r.t O-atom.
There are four types of bonds present in a CH3CH2OH molecule i.e., a C-C bond, five C-H bonds, one C-O bond, and an O-H bond.
The C-C bond is purely non-polar.
The C-H bond is slightly polar (almost non-polar as per Pauling’s electronegativity scale). Contrarily, the C-O and O-H bonds are strongly polar due to the electronegativity differences of 0.89 units and 1.24 units between the bonded atoms respectively.
The strong C-O and O-H dipole moments and the small C-H dipole moments do not get canceled in the bent or angular molecular shape.
CH3CH2OH is thus overall polar (net µ > 0).
Why is CH3CH2CH3 non-polar while CH3CH2OH is polar?
Propane (CH3CH2CH3) only consists of non-polar C-C bonds and very weakly polar C-H bonds.
The molecule possesses a symmetrical tetrahedral shape. The central C-atom having two H-atoms and two CH3 groups lying on each side.
CH3CH2OH consists of strongly polar C-O and O-H bonds in addition to the C-C and C-H bonds present in it.
The dipole moments of individually polar bonds do not get canceled in the asymmetric bent shape of the molecule. It is thus overall polar (net µ> 0).
Which one is more polar? CH3CH2OH or CH3OH?
Both ethanol (CH3CH2OH) and methanol (CH3OH) are polar molecules belonging to the alcohol family, owing to the presence of a strongly polar hydroxyl (O-H) functional group in these.
However, CH3OH is more polar than CH3CH2OH owing to a shorter alkyl chain in the former.
A C-C bond present in CH3CH2OH is purely non-polar; similarly, the C-H bonds are also very weakly polar (almost non-polar as per Pauling’s electronegativity scale).
No such C-C bond is present in CH3OH.
The length of the alkyl chain is inversely related to the polarity of an organic molecule.
Which isomer is more polar? CH3OCH3 or CH3CH2OH?
CH3OCH3 and CH3CH2OH are isomers of each other as they possess the same molecular formula (C2H6O) but a different structural arrangement.
Both molecules possess a bent or V-shape w.r.t the O-atom.
Ethanol (CH3CH2OH) is more polar than dimethyl ether (CH3OCH3).
CH3CH2OH consists of weakly polar C-H bonds, a polar C-O bond and an extremely polar O-H bond.
Contrarily, CH3OCH3 comprises weakly polar C-H bonds and two relatively more polar C-O bonds.
However, the C-O bonds present in CH3OCH3 are comparatively less polar than the O-H bond in CH3CH2OH.
The bonded atoms have an electronegativity difference of 0.89 units in a C-O bond as opposed to a difference of 1.24 units in the O-H bond.
Smaller individual dipole moments lead to an overall lower net dipole moment value.
Ethanol (CH3CH2OH) is a polar molecule (net µ > 0).
CH3CH2OH comprises a purely non-polar C-C bond, five weakly polar C-H bonds, a polar C-O bond, and a strongly polar O-H bond.
The CH3CH2OH molecule has a tetrahedral shape w.r.t C-atom while it possesses a bent, angular, or V-shape w.r.t the O-atom.
Oxygen being highly electronegative, strongly attracts the C-C and C-H bonded electrons towards itself, in addition to attracting the C-O and O-H shared electron cloud.
The individual C-H and O-H dipole moments do not get canceled in the asymmetrical shape of the molecule. The charged electron cloud stays non-uniformly spread over the molecule, which leads to a polar CH3CH2OH molecule with a permanent dipole moment value.
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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