Propane is a saturated paraffin hydrocarbon with the chemical formula C3H8. It exists as a colorless, odorless gas at room temperature. C3H8 is an extremely flammable compound and a potential liquid petroleum gas ingredient (LPG).
Different blends of propane, such as iso-propane, are used as refrigerants.
Continue reading the article to determine whether propane (C3H8) is polar or non-polar.
Is C3H8 polar or non-polar?
Propane (C3H8) is a non-polar molecule. Each C-H bond in the C3H8 molecule is non-polar due to a slight electronegativity difference between the bonded atoms. Each C-C bond is also non-polar due to no electronegativity difference between them.
The electronegativity of the carbon (C) atom is only slightly more than the hydrogen (H) atom. There is almost equal sharing of the electron cloud in the C-H bond due to this slight electronegativity difference.
Thus, each C-H and C-C bond in the C3H8 molecule is non-polar and possesses no dipole moment value.
Also, due to the symmetrical tetrahedral geometry of C3H8, the net dipole moments (µ), if any, will be canceled. Therefore, Propane (C3H8) is said to be a nonpolar molecule.
A molecule with an equal charge distribution between different centers of bonded atoms is a non-polar molecule, such as a C3H8 molecule.
It is formed by the covalent bond between two same atoms leading to a symmetric electron density in the molecule overall.
In the case of asymmetric molecules, If the dipole moments of individually polar bonds are canceled, the molecule will be non-polar.
Hence a non-polar molecule has an equal distribution of the electronic charge. Contrarily, if the electronic charge is not evenly distributed over the molecule, in that case, it will be a polar molecule.
The following three factors influence the polarity of any covalent molecule:
Electronegativity.
Dipole moment.
Molecular geometry or shape.
In the next section, we will discuss how these three factors lead to the non-polar nature of the C3H8 molecule.
Factors affecting the polarity of C3H8
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 the bonded atoms in a molecule, the higher the bond polarity.
Hydrogen belongs to group 1-A (or 1) of the Periodic Table. The electronic configuration of hydrogen is 1s1, so it has 1 valence electron.
On the other hand, carbon belongs to group IV-A (or 14) of the Periodic Table. The electronic configuration of carbon is 1s2 2s2 2p2, so it has 4 valence electrons available for bonding.
The eight H-atoms thus form eight single covalent bonds with the three C-atoms on each side of the C3H8 molecule. Besides, there are two C-C single covalent bonds.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Carbon (6C)
1s22s22p2
4
According to the Pauling scale, a bond is polar covalent if the molecule’s electronegativity difference in bonded atoms ranges from 0.5 to 1.6 units. An electronegativity difference of less than 0.5 indicates the non-polarity of a covalent bond.
Carbon (E.N = 2.55) is slightly more electronegative than hydrogen (E.N = 2.2). An electronegativity difference of only 0.35 units is present between the C-H bonds in the C3H8 molecule.
Also, no electronegativity difference exists between the carbon atoms in the C-C bonds (∆E.N = 0).
Due to the slight electronegativity difference, there is almost equal sharing of the electron cloud between the bonded C and H atoms in the C3H8 molecule. Each C-C bond also has an equal sharing of electrons due to no electronegativity difference between the bonded atoms.
Consequently, each C-H and C-C bond in the C3H8 molecule is non-polar, leading to the overall non-polarity of the Propane molecule.
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 any molecule depends on the difference in electronegativity between the bonded atoms. The greater the electronegativity difference, the higher the bond polarity, resulting in a high dipole moment value.
It points from the partial positive (δ+) center to the partial negative (δ–) center of a bond or molecule.
As each C-H and C-C bond in the C3H8 molecule is non-polar due to very little to no electronegativity difference, each bond has no dipole moment value.
Thus, the C3H8 molecule is non-polar due to zero dipole moment overall.
Molecular geometry
As discussed earlier, a propane (C3H8) molecule consists of eight single C-H and two single C-C covalent bonds. The overall molecule consists of a total of 20 valence electrons.
According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, C3H8 is an AX4-type molecule with respect to every carbon atom. Around each central C-atom, there are 4 bond pairs of electrons.
There are no lone pairs of electrons on the central atom, so the propane (C3H8) molecule experiences no distortion in its shape.
Due to the absence of disorientation due to no lone pairs on the central C-atom, the C3H8 molecule has a symmetrical tetrahedral shape. The C-C-C bond angle is 111.6°, and the C-C-H bond angle is 109.5°.
As a result, even if dipole moments are generated on each side along the C-H and C-C bonds, they will cancel out each other, making C3H8 a non-polar molecule.
In conclusion, C3H8 is a non-polar molecule with a net dipole moment value equal to zero.
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), nitric oxide (NO), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), ethane (C2H6), propane (C3H8), etc.
According to the Pauling scale, a bond is non-polar covalent if a molecule’s electronegativity difference in bonded atoms ranges less than 0.5 units.
The individual C-H bonds in the C3H8 molecule are non-polar due to an electronegativity difference of only 0.35 units between C and H atoms.
Each C-C bond is also non-polar, as there is no electronegativity difference between the bonded C atoms.
The molecule (C3H8) overall is non-polar because it has a symmetric tetrahedral geometry.
The individual dipole moments, if any, get canceled in opposite directions. So, net µ becomes zero in the molecule.
Thus, C3H8 is a non-polar molecule with a zero net dipole moment.
Compare the polarity of C3H8 and C3H8O molecules.
All the bonds (C-H and C-C) in the C3H8 molecule are non-polar due to little to no electronegativity difference between the bonded atoms.
The dipole moment of each C-H and C-C bond, if any, will be canceled out of each other in the symmetrical tetrahedral structure.
Thus, C3H8 is non-polar.
As the carbons in the C3H8O molecule are bonded to different atoms, all the bonds (C-H, C-C, and C-OH) are not symmetrical.
The dipole moments of the bonds do not cancel out each other.
Thus, C3H8O is polar.
Is propane (C3H8) soluble in water?
It is a general principle that “Like dissolves like”.
Water is a polar molecule, while propane is a non-polar molecule.
Water molecules are attracted to other molecules through hydrogen bonding. Non-polar molecules like propane do not have a dipole moment and therefore do not engage in hydrogen bonding. As a result, they are not soluble in water.
Is there a formal charge on the bonded atoms in the C3H8 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For hydrogen atoms
Valence electrons = 1
Bonding electrons = 2
Non-bonding electrons = 0
∴ The formal charge on the hydrogen atoms = 1-0-2/2 = 1-1 = 0
For carbon atoms
Valence electrons = 4
Bonding electrons = 8
Non-bonding electrons = 0
∴ The formal charge on the central carbon atoms = 4-0-8/2 = 4-4 = 0
Thus, no formal charge is present on the propane (C3H8) molecule.
Summary
Propane (C3H8) is a non-polar molecule.
The individual C-H bonds are non-polar due to an electronegativity difference of only 0.35 units between the bonded atoms.
The C-C bonds are also non-polar, as there is no electronegativity difference between the bonded atoms (∆E.N = 0).
Due to the symmetric tetrahedral molecular geometry of the C3H8 molecule, the dipole moments of the individual C-C and C-H bonds, if any, will be canceled in opposite directions.
In conclusion, C3H8 is a non-polar molecule with net µ =0.
The C-C-C bond angle is 111.6°, and the C-C-H bond angle is 109.5°.
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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