CF2Cl2 is a polar molecule due to the electronegative difference between Fluorine (3.98), Chlorine (3.16), and Carbon (2.55). Fluorine and Chlorine have more electronegativity so they pull electrons from the central carbon atom. As a result, the partial positive charge on carbon atom and negative charge on fluorine and chlorine atoms.
Detailed Explanation: Why is CF2Cl2 a Polar Molecule?
CF2Cl2 which chemical name is dichlorodifluoromethane, mostly used as a refrigerant and fire retardant. Its molecular mass is around 120.91 g/mol and vapor pressure is 568kPa.
Before entering into its polarity, let’s have some basic ideas about polar and nonpolar molecules,
Polar molecules are defined as the presence of polar bond within the molecule or have irregular geometry (not symmetrical structure) so that the net dipole moment of molecule can’t be zero as the center of gravity of negative charge and positive charge is separated by a small distance. In the absence of an electric field, the moment of polar molecules in dielectric substances are randomly oriented but as soon as the electric field is applied, it tends to align along the direction of the field.
These molecules are used to show little ionic as well as covalent characteristics i.e. they are soluble in water, can conduct electricity, have the strong electrostatic force and many ionic characteristics despite having covalent bonds.
Example of Polar molecules: Water (H2O), Hydrochloric acid (HCl), Ammonia (NH3) etc.
Nonpolar molecules are considered as pure covalent bonded molecules which are formed by mutual sharing of electrons and have a net dipole moment zero. In nonpolar molecules, there is no occurrence of partial positive and negative charge on the atoms because of the same electronegativity different between the atoms ( Homonuclear diatomic molecules like H2, O2, N2, etc) or molecule has regular geometry (symmetrical molecules like CCl4, CO2, etc) so bond polarities are canceled by each other.
When Nonpolar molecules are placed in an electric field, the center of gravity of positive charge moves in direction of the field and the center of the gravity of negative charge in opposite direction. This separation between positive and negative charges continues until the applied external force and internal force are balanced.
Example of Nonpolar molecules: All diatomic molecules (H2, N2, O2, Cl2, etc.), Carbon tetrachloride (CCl4), Carbon Dioxide (CO2), etc.
Freon-2 (CF2Cl2) Polar or Nonpolar (based on characteristics)
CF2Cl2 is a polar molecule and the Fluorine atom closest to the negative side as fluorine is highly electronegative than both chlorine and carbon. F atom attracts the electrons from central carbon as a result, formation of partial positive charge on carbon and negative charge on fluorine and the same in case of carbon-chlorine bonding.
Here’s some of the characteristics of CF2Cl2 which explain why it is considered as a polar molecule point-to-point:
Electronegativity is the tendency of an atom to attract lone pair of electrons at the time of bond formation. The atoms having high electronegativity value pull the shared pair of electrons closer from the atoms having low electronegativity value. As a result, induced negative and positive dipole poles on the molecules.
In CF2Cl2 molecule,
Electronegativity of Fluorine= 3.98
Electronegativity of Chlorine= 3.16
Electronegativity of Carbon= 2.55
Now according to the Pauli scale, if the electronegativity difference between two bonding atoms is within 0.5 to 2.0, that bond is polar. Here in CF2Cl2, the electronegativity difference between fluorine and carbon is 1.43 and between chlorine and carbon are 0.61. so that both F-C and Cl-C bonds are polar covalent bonds.
Also Read: Is XeF2 Polar or Nonpolar?
Lewis Structure & Molecular Geometry
CF2Cl2 is made up of three distinct atoms C, Cl, and F. here total of 32 valence electrons participate in molecule formation in which central atom carbon has only 4 valence electrons sharing two-two electrons with each fluorine and chlorine. Both fluorine and chlorine have extra three lone pair of electrons and they do not participate in bond formation.
Due to two distinct atoms are attached with central carbon atom having different dipole charges and electronegativity value, the molecule has tetrahedral geometry unlike carbon tetrachloride which has symmetrical geometry due to the central carbon atom has four same chlorine atoms attached. And this is the main reason why CF2Cl2 is a polar molecule as net dipole moment doesn’t cancel.
Dipole moment arises when there is an electronegativity difference between two atoms within a molecule. Basically, the dipole moment is the product of charges induced on either side of the molecule and distance of separation. Dipole moment is denoted by ‘µ’ and given be,
Dipole moment (µ)= Charge (Q) * distance of separation (r)
It is measured in Debye units denoted by ‘D’. 1 D = 3.33564 × 10-30 C.m, where C is Coulomb and m denotes a meter.
Dipole moment is a vector quantity and depends on the resultant of dipole charges i.e. if the molecule has symmetrical geometry, the net dipole moment will be zero. But CF2Cl2 has tetrahedral geometry which is not symmetrical so the dipole charges do not cancel out each other and the molecule has a net dipole moment which makes CF2Cl2 a polar molecule.
Electron density is the probability of an electron to find at a specific location within an atom or molecule. According to the uncertainty principle, it is impossible to find out the exact location of an element at a particular time within a molecule or atom. But chances of finding an electron is higher with the higher electron density atom which means the atom having more electrons closing to it, chances of finding an electron is high.
In CF2Cl2, Fluorine and Chlorine have high electron density compared to carbon due to their higher electronegativity value. Especially, Fluorine has higher electron density so the probability of finding an element is higher here.
The solubility principle is based on “like dissolves like” which means similar groups of molecules are dissolved in a similar type of solvents. If a molecule is polar, more likely it will dissolve in a polar solvent and same in the case of nonpolar molecules also. So that CF2Cl2 is also soluble in only polar solvents like water (H2O), ammonia (NH3), etc. and insoluble in nonpolar solvents like carbon tetrachloride (CCl4), pentane, hexane, etc.
Preparation of CF2Cl2
Synthetically, Dichlorodifluoromethane (CF2Cl2) is prepared by the reaction of carbon tetrachloride (CCl4) with hydrogen fluoride gas (H2F2) in the presence of catalyst SbF5 most of the time. It is commercially sold in the market under the name of Freon-12 and Chlorofluorocarbon halomethane (CFC).
Properties of CF2Cl2
1. It is a colorless gas with ether-like odor at a higher concentration level.
2. It has a very low melting point -157.7 °C and a boiling point -29.8 °C and it is soluble in polar solvents like water, alcohol, benzene, acetic acid, and more.
Uses of CF2Cl2
- It is used as a refrigerant in the refrigerator and also as an air conditioner in vehicles.
- It is used as an aerosol spray propellant.
- Used in submarines and aircraft as fire-retardant.