CH2F2 is the chemical formula for difluoromethane. It is a colorless gas with an ambient atmosphere and is slightly soluble in water, with high thermal stability. It has a molar mass of 52.02 g/mol. Difluoromethane is used in refrigerators, air conditioners, plasma etching, and as a heat transfer fluid.
To find out whether the difluoromethane (CH2F2) molecule is polar or non-polar, continue reading this article.
Is CH2F2 polar or non-polar?
Difluoromethane (CH2F2) is a polar molecule. It consists of one carbon (C) atom, two hydrogens (H) atoms, and two fluorine (F) atoms. The carbon is kept at the central position, and the other atoms are at the surrounding positions, making a regular tetrahedral molecular shape and geometry.
An electronegativity difference of 1.43 units exists between a carbon and a fluorine atom in the C-F bond in the CH2F2 molecule. Thus, both C-F covalent bonds are individually polar in the CH2F2 molecule and possess a specific dipole moment value (symbol µ).
The C-H bonds are only weakly polar due to an electronegativity difference of 0.35 units between the bonded carbon and hydrogen atoms.
Although the CH2F2 molecule is tetrahedral in shape, still the strong dipole moment of the C-F bonds does not get canceled with the weak dipole moments of C-H bonds that are almost non-polar.
As a result, CH2F2 has a permanent dipole moment and is overall polar (net µ =1.97 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 difluoromethane (CH2F2) is overall a polar molecule.
Factors affecting the polarity of CH2F2
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
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 in its only shell, and it lacks one more electron to complete its outer electron shell.
Conversely, fluorine (F) is a halogen present in Group VII A of the Periodic Table. The electronic configuration of fluorine is 1s2 2s2 2p5. According to this electronic configuration, an F-atom has 7 electrons in its valence shell, and it lacks one more electron to complete its octet electronic configuration.
Hence in CH2F2, the central C-atom is bonded with H-atoms, and F-atoms via four single covalent bonds. The Lewis dot structure contains two C-H bonds and two C-F bonds.
All 4 valence electrons of carbon get consumed in covalent bonding; thus, there is no lone pair of electrons present on it.
Contrarily both F-atoms contain 3 lone pairs of electrons in the CH2F2 Lewis structure.
In this way, all bonded atoms attain a completely stable electronic configuration via lone pairs and chemical bonding in CH2F2.
As there are no lone pairs of electrons on the central C-atom in CH2F2 so, there is no distortion witnessed in its shape and/or geometry.
Atom
Electronic configuration
Valence electrons
Carbon (6C)
1s22s22p2
4
Hydrogen (1H)
1s1
1
Fluorine (9F)
1s22s22p5
7
The electronegativity difference between a C-atom (E. N= 2.55) and an H-atom (E. N= 2.20) in each C-H bond is 0.35 units. Due to the small electronegativity difference, the C-H bonds are considered weakly polar or almost non-polar in CH2F2.
Contrarily, the more electronegative F-atoms (E. N= 3.98) strongly attract the shared electron cloud away from the central C-atom (E. N= 2.55) in each C-F bond present in CH2F2.
Thus, the fluorine atom present in the CH2F2 molecule gains a partial negative (Fδ-) charge, while the central carbon atom obtains a partial positive (Cδ+) charge.
As a result, with an electronegativity difference of 1.43 units, each C-F bond is strongly polar in the CH2F2 molecule.
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 charges 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.
So in CH2F2, the dipole moment of each polar C-F bond points from Cδ+ to Fδ-(as shown below).
Fluorine being strongly electronegative, not only attracts the C-F bonded electrons but also attracts the shared electron pair from each C-H bond.
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, CH2F2 is an AX4E0 or simply AX4-type molecule. To one C-atom at the center (A), four bonded atoms are attached (two H-atoms and two F-atoms), and the central C-atom contains no lone pair (E).
So, the molecular geometry or shape of CH2F2 is identical to its ideal electron pair geometry, i.e., tetrahedral.
To minimize the repulsions and to attain stability in the tetrahedral structure of CH2F2, the approximate bond angles are ∠F-C-H = 109°, ∠H-C-H = 113°, and ∠F-C-F = 108.5°.
Although due to the absence of any lone pair of electrons on the central C-atom, the CH2F2 molecule has a regular tetrahedral shape; still, the dipole moments of the C-F bonds do not cancel out because due to smaller electronegativity difference, the C-H bonds are almost non-polar.
Hence, the weak dipole of C-H is unable to cancel the strong dipole of C-F bonds. Consequently, in CH2F2, there is a permanent dipole moment, and the molecule is overall polar (net µ = 1.97 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), phosphorus trifluoride (PF3), difluoromethane (CH2F2), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), ethane (C2H6), propane (C3H8), etc.
The C-F bonds are strongly polar due to an electronegativity difference of 1.43 units between the bonded atoms. However, the C-H bonds are only weakly polar due to a small electronegativity difference of only 0.35 units between the bonded atoms.
CH2F2 has a tetrahedral geometry; still, the strong dipole moment of the two C-F bonds does not get canceled with the weak dipole moments of the C-H bonds.
The charged electron cloud stays non-uniformly distributed over the molecule.
Thus, CH2F2 is overall a polar molecule with a net dipole moment µ = 1.97 D.
Why is CH2F2 a polar molecule even though it has a tetrahedral shape?
CH2F2 is a polar molecule because the shared electron cloud is not symmetrically distributed over the tetrahedral shape of the molecule.
Halogen atoms are highly electronegative, so the F-atom (E. N= 3.98) present in CH2F2 attracts the shared electron cloud of the C-H bonds in addition to attracting C-F bonded electrons.
The dipole moment of individually polar C-F bonds does not get canceled by that of C-H bonds in CH2F2 overall, so it is a polar molecule.
CH4 and CH2F2 are both tetrahedral molecules, but CH2F2 is polar, while CH4 is non-polar. Why?
Methane (CH4) is made up of four equivalent C-H bonds. Carbon is slightly more electronegative than hydrogen, so the C-H bond is weakly polar.
Due to the symmetrical shape of CH4, the dipole moment of these weakly polar C-H bonds gets canceled in opposite directions. Thus, CH4 is a non-polar molecule, (net µ =0).
In comparison, difluoromethane (CH2F2) comprises two C-H and two C-F bonds. The molecule also has a tetrahedral shape.
Still, the dipole moment of the C-F bonds does not get canceled by weakly polar C-H bonds. Consequently, CH2F2 has a permanent dipole moment and is overall a polar molecule (net µ =1.97 Debye).
Which is more polar, CH2Cl2 or CH2F2?
CH2F2 (net µ =1.97 D) is more polar than CH2Cl2 (net µ =1.67 D).
Both the molecules have an asymmetric tetrahedral shape containing two C-H bonds and two C-X bonds where X= halogen atom. However, the difference in polarity exists due to the electronegativity difference between bonded atoms.
Fluorine (F) is the most electronegative element of the periodic table. Electronegativity decreases down the group, so chlorine (Cl) is less electronegative than F.
Accordingly, there is a higher electronegativity difference (1.43 units) between the bonded atoms in a C-F bond, so it possesses a higher dipole moment as opposed to a C-Cl bond, which possesses an electronegativity difference of only 0.61 units between the bonded atoms.
Higher individual dipole moments lead to a higher net dipole moment, thus greater molecular polarity.
Is there a formal charge on the bonded atoms in the CH2F2 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
All atoms in the CH2F2 molecule, including carbon, hydrogen and fluorine, obtain a formal charge equal to zero; hence there are no or zero formal charges present on the difluoromethane molecule overall.
Summary
Difluoromethane (CH2F2) is a polar molecule.
It consists of two almost non-polar C-H bonds with an electronegativity difference of 0.35 units and two strongly polar C-F bonds due to an electronegativity difference of 1.43 units between the bonded atoms.
Difluoromethane CH2F2 has an identical electron and molecular geometry or shape i.e., tetrahedral with bond angles ∠ F-C-H = 109°, ∠ H-C-H = 113°, and ∠ F-C-F = 108.5°.
Due to the absence of any lone pair of electrons on the central C-atom, there is no distortion in the shape and geometry of CH2F2.
The weak dipole moments of C-H bonds are unable to cancel the strong dipole of C-F bonds.
Fluorine is highly electronegative and attracts the shared electron cloud from each C-F bond in addition to attracting C-H bonded electrons.
Consequently, the charged electron cloud stays non-uniformly spread over the molecule. CH2F2 has a permanent dipole of 1.97 D,so it is overall a polar molecule.
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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