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.
Polar 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
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 Different
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.
Dipole Moment
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
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.
Solubility Principle
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.
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