Nitrogen Dioxide (NO2) is a polar molecule because of the electronegativity difference between Oxygen and Nitrogen and also irregular bent geometry of NO2 molecule due to the presence of a pair of nonbonding electrons on the central nitrogen atom. Therefore, both N-O bonds polarity in Nitrogen Dioxide is not canceled by each other as a molecule is asymmetrical.
Detailed Explanation: Why is NO2 a Polar molecule?
Nitrogen Dioxide which chemical formula is NO2. Mostly uses in the production of fertilizer because it is a major component of chlorophyll. It mostly acts as an oxidizing agent in the redox reactions as it belongs to one of the highly reactive groups of nitrogen oxide (NOx) and its oxidation number is +4.
Before going further into its polarity nature, let's know some basic ideas about what polar and nonpolar molecules are,
Polar Molecules
Polar molecules are simply defined as the presence of polar
bonds within the molecule or have irregular geometry (not symmetrical structure), so the net dipole moment of the molecule is not 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 under the influence of the electrical field it tends to
align along the direction of the field.
These molecules are used to show little ionic
characteristics i.e. they are soluble in water, can conduct electricity, have
strong electrostatic force and many more.
Examples of Polar molecules: Water (H2O), Hydrochloric acid(HCl), Ammonia (NH3), etc.
Nonpolar Molecules
Nonpolar molecules are simply pure covalent bonded molecules
with mutual sharing of electrons and have net dipole moment zero. As there are
no occurrence of partial positive and negative charge on the atoms because of the same electronegativity difference between the atoms (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 the direction of the field, and the center of the gravity of negative charge moves in the 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.
Nitrogen Dioxide (NO2) Polar or Nonpolar (Basis of Characteristics)
NO2 is a polar molecule and the Oxygen atom closest to
negative side as the electronegativity of Oxygen (3.44) is comparatively greater
than Nitrogen (3.04) so that Nitrogen has a partial positive charge and Oxygen
has a partial negative charge established within the molecule.
These are some of the characteristics of Nitrogen Dioxide to
prove why NO2 is considered as a polar molecule,
Electronegativity Difference
Electronegativity is the tendency to attract shared pair of
electrons of an atom within a molecule. NO2 has two distinct elements Nitrogen
and Oxygen, have E.N 3.04 and 3.44 respectively.
According to Pauli Scale, the electronegativity difference between two atoms in a molecule is within 0.4 to 1.7, it is considered a polar
molecule if the bond polarity is not canceled. In this case, the electronegativity
difference between Oxygen and Nitrogen is 0.4 which indicates the molecule is
polar.
Also Read: Is XeF4 Polar or Nonpolar?
Lewis Structure & Molecular Geometry
In NO2, a total of 17 valence electrons participating is in molecule formation in which one lone electron does not participate in bonding. This extra electron on the nitrogen atom exerts repulsion on both Oxygen atoms resulting in bent molecular geometry of Nitrogen Dioxide.
Due to the presence of unbonded electrons on the nitrogen atom, the Oxygen atoms are widely spread as result the bond angle is 134.3° instead of idle 120°. This makes the molecule asymmetrical, thus bond polarity does not cancel by each other.
Dipole Moment
Dipole Moment arises when the electronegativity difference between two atoms as a result of the formation of a partial positive charge on the less electronegative atom and partial negative charge on the higher electronegative atom.
Here in this case there is a difference in E.N and also
molecular geometry is irregular (asymmetrical) so that the net dipole moment is
not zero. The net dipole moment is calculated as a product of distance between the
atoms and partial charge on either one of the atoms (neglect positive or negative
sign).
Electron Density
Electron density is the probability of an electron being
present at a dedicated location. But if there is an electronegativity difference
between two atoms in a molecule, the electron density is higher towards the
higher E.N atom. Which causes a slightly partial negative on the nearby atom and a slightly partial positive charge on the opposing atom takes place.
Solubility Principle
As we know, Polar molecules are soluble in polar solvents and Nonpolar molecules are soluble in Nonpolar solvents in most cases (some exceptions always exist). Moreover, pure covalent (Nonpolar) molecules are not soluble in water but No2 is soluble in water and many other polar solvents.
Sources of Nitrogen Dioxide
The major source of NO2 is the combustion of fossil fuels which
includes coal, petrol, gas, diesel, and different fuels. It is also produced
synthetically at the time of the explosion, welding, petrol refining. Its natural
sources are volcanoes, lightning strikes, oceans, biological decay.
This has slowly become a threat for living organisms on earth
as every year we are adding more than 30 million tons of Nitrogen Dioxide to the atmosphere in the form of pollutants.
Properties of NO2 Molecules
1. No2 has a Melting point of -9.3 °C and a Boiling point of 21.15 °C. At higher temperatures, it is a reddish-brown gas.
2. NO2 is dimerized, acidic in nature, electron-withdrawing
group, paramagnetic, meta directing.
3. Nitrogen Dioxide is a toxic gas because it is soluble in
water vapor and so that it can easily enter inside the lung through inhalation
and hydrolysis to nitrous and nitric acid in form of free radicals which cause Pulmonary
edema and inflammation of the bronchioles.
Uses of Nitrogen Dioxide
- Mostly uses for the production of fertilizers in large amounts.
- uses for the preparation of nitric acid and sulphuric acid in the laboratory.
- As a catalyst in many chemical reactions of oxidation and also used as a strong oxidizing agent.
- For distillation to prevent polymerization of acrylates.
- It is used in spacecraft mostly as a rocket fuel because of it's high combustion capacity.
- It is frequently used as a bleaching agent.
Post a Comment