Methyl fluoride is an important hydrofluorocarbon with the chemical formula CH3F. It is a colorless, non-toxic, and flammable gas at room temperature. It is also known as Freon-41 and HFC-41.
The IUPAC name of CH3F is fluoromethane. It is used as a refrigerant and as an etching gas in plasma etch reactors.
What is the nature of the chemical bond present in fluoromethane (CH3F)? Is it a polar or a non-polar molecule? Let’s find out in this detailed article.
Is CH3F polar or non-polar?
Methyl Fluoride (CH3F) is a polar molecule. The central carbon (C) atom in the CH3Fmolecule is surrounded by three hydrogens (H) atoms and a fluorine (F) atom via single covalent bonds, forming an asymmetric tetrahedral molecule.
The electronegativity of the fluorine (F) atom is greater than the carbon (C) and hydrogen (H) atoms. The higher electronegative F atoms attract the shared electron pairs with more influence in the CH3F molecule.
Thus, all the bonds are individually polar and possess a specific dipole moment value.
The asymmetric tetrahedral shape of CH3F further enhances the polarity effect as the dipole moments of the bonds do not get canceled in the molecule overall. Thus, CH3F is a polar molecule with a net dipole moment value > 0.
In chemistry, a molecule with unequal charge distribution between different centers of bonded atoms is a polar molecule.
It is formed by the covalent bond between two different atoms leading to an asymmetric electron density.
In this case, the atoms acquire partial positive (δ+) and partial negative (δ–) charges.
If the dipole moments of individually polar bonds are not canceled due to the asymmetrical shape of the molecule, the molecule will be polar, such as CH3F.
Hence a polar molecule has an unequal distribution of the electronic charge. Contrarily, if the electronic charge is evenly distributed over the molecule, in that case, it will be a non-polar molecule overall.
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 factors lead to the polarity of the CH3F molecule.
Factors affecting the polarity of CH3F
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.
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.
On the other hand, fluorine belongs to group VII-A (or 17) of the Periodic Table. The electronic configuration of fluorine is 1s2 2s2 2p5, which hints at the presence of 7 valence electrons.
The three H-atoms and one F-atom thus form a single covalent bond with the central C-atom on each side of the CH3F molecule.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Fluorine (9F)
1s22s22p5
7
Carbon (6C)
1s22s22p2
4
The electronegativity of fluorine is more electronegative than the carbon and hydrogen atoms (E.N of F = 3.98, E.N of C = 2.55, E.N of H = 2.2).
Due to this electronegativity difference, the F-atom strongly attracts the shared electron cloud from the bonds. The bonded electrons are held significantly close to the fluorine atom in the CH3F molecule.
The central C-atom and H-atoms thus gain a partial positive charge (Cδ+ and H δ+), while the fluorine atom being more electronegative, obtains a partial negative (Fδ-) charge. In this way, oppositely charged poles develop in the CH3F molecule.
The F atoms not only attract the shared electron cloud of each C-F bond but also attracts C-H electrons. As a result, the electron cloud distribution in the molecule is unequal overall.
Thus, CH3F is a polar 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.
The difference in electronegativity between the bonded atoms in the CH3F molecule leads to dipoles pointing from Cδ+and Hδ+ to Fδ-.
Thus, each bond in the CH3F molecule is polar, with a net dipole moment greater than 0.
Molecular geometry
As discussed earlier, a methyl fluoride (CH3F) molecule consists of three single C-H covalent bonds and one C-F covalent bond. There are a total of 14 valence electrons in the overall molecule.
According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, CH3F is an AX4-type molecule. Around the central carbon atom (A) are four bond pairs (X).
To minimize the electronic repulsions between the atoms, the methyl fluoride (CH3F) molecule adopts a tetrahedral geometry with a bond angle of 109.5°.
As a result of the asymmetric arrangement of atoms around the central carbon, the individual dipole moments of the bonds do not get canceled in the methyl fluoride (CH3F) molecule. There is an unequal distribution of electronic charge over the molecule.
In conclusion, CH3F is an overall polar molecule with a net dipole moment (µ = 1.847 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 fluoride (CH3F), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.
Due to a great electronegativity difference between the bonded fluorine (F), hydrogen (H), and carbon (C) atoms, polar covalent bonds are generated in the CH3F molecule.
Due to the unsymmetrical arrangement of atoms in the tetrahedral molecule, the individual dipole moments of the bonds are not canceled.
Thus, CH3F is a polar molecule.
Fluorine is more polar than chlorine, yet the dipole moment of CH3Cl is greater than CH3F. Why?
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms (µ = Q.r)
Due to the larger charge separation in the CH3Cl molecule, the C-Cl bond length (178 pm) is greater than the C-F bond length (139 pm).
This increased bond length results in a higher dipole moment value of CH3Cl.
Thus, the dipole moment of the CH3Cl molecule is greater than the CH3F molecule.
Compare the polarity of CH3F and CH3I molecules.
The greater the electronegativity difference between the bonded atoms, the higher the bond polarity, resulting in a high dipole moment value.
Fluorine ( E.N = 3.98) is more electronegative than the iodine atom (E.N = 2.66).
Thus, fluorine will attract the shared electron pairs in the CH3F molecule with more influence than the iodine atom in the CH3I molecule.
As a result, the C-F bond will be more polar than the C-I bond. Thus, CH3F is more polar than the CH3I molecule.
Is there a formal charge on the bonded atoms in the CH3Fmolecule?
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 fluorine atom
Valence electrons = 7
Bonding electrons = 2
Non-bonding electrons = 6
∴ The formal charge on the fluorine atom = 7-6-2/2 = 1-1 = 0
For carbon atom
Valence electrons = 4
Bonding electrons = 8
Non-bonding electrons = 0
∴ The formal charge on the central carbon atom = 4-0-8/2 = 4-4 = 0
Thus, no formal charge is present on the methyl fluoride (CH3F) molecule.
Summary
Methyl fluoride/fluoromethane (CH3F) is a polar molecule.
Due to a great electronegativity difference between fluorine, hydrogen, and carbon, polar covalent bonds are generated.
The fluorine atom attracts the shared electron cloud strongly from the CH3F molecule.
The difference in electronegativity between the bonded atoms leads to dipoles pointing from C δ+and Hδ+ to F δ-.
The AX4-type CH3F molecule adopts a tetrahedral geometry.
Due to the unsymmetrical arrangement of atoms in the tetrahedral molecule, the individual dipole moments of the bonds are not canceled in the molecule overall. Thus, CH3F is a polar molecule (μ = 1.8 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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