O3, also known as ozone is a very famous chemical compound in our chemistry textbooks. Ozone or trioxygen is the inorganic compound present in Earth’s atmosphere that saves us from harmful ultraviolet rays coming from the Sun. There is a very famous question regarding whether O3 is polar or non-polar.
In this article, I’ll explain the answer to this question in detail and we will try to learn about the chemical structure of the O3 molecule.
So, is O3 polar or non-polar? O3 is a polar molecule and it is due to its bent molecular geometry. In O3, the electric dipole moments of the bonds don’t counterbalance one another which results in a net dipole moment. Due to this, O3 (Ozone) is polar in nature.
Let’s study this in detail.
Molecular Structure of O3
Let’s first look at the Lewis structure of O3. Oxygen (O) has an atomic number of 8 and there are 6 electrons in its valence shell.
The middle Oxygen atom shares 4 electrons to form 1 double bond and 1 single bond with the other 2 oxygen atoms.
Sometimes people get confused that if middle oxygen makes 1 double bond and 1 single bond with other 2 oxygen atoms, then there should be 3 unbonding electrons left on it. But in reality, there are just 2 unbonding electrons left on the middle oxygen atom.
It is because the O3 has 2 resonance structures that keep resonating and double bond and single bond forms alternatively at both sides. Both of these structures are shown in the figure shown above.
Hence, Middle Oxygen atom is left with 1 lone pair of electrons. Also, the lone pair provides greater repulsion to bond pairs on both sides, O3 molecular geometry comes out to be bent. The angle between its bond pairs comes out to be 116 degrees.
Due to the lone pair-bond pair repulsion, the O3 molecule is bent in shape which results in a net dipole that imparts polarity in the molecule.
Why is O2 non-polar but O3 polar?
In the O2 molecule, 2 oxygen atoms are joined together with a double bond between them. Each of these atoms has 2 lone pairs on each other but as there are only 2 atoms in this molecule, O2 is linear in shape.
Also, the atoms are the same i.e Oxygen atom hence, there is no net dipole moment in the molecule. Therefore, the O2 molecule comes out to be non-polar.
But the case of O3 is different as there are 3 atoms due to which it has a bent shape. This bent shape results in net electric dipole which imparts polar nature in the O3 molecule.
The Ozone molecule does not maintain any symmetry, it is bent in shape due to unequal lone pairs on all the oxygen atoms.
It is very well known that lone pair-lone pair repulsion is greater than bond pair-bond pair and lone pair-bond pair repulsion. Therefore, Oxygen atoms in Ozone face lone pair-lone pair repulsion that leads to a bent shape.
The outer oxygen atom that is connected to the central atom has a partial negative charge as it contains more lone pairs than other Oxygen atoms. While the center Oxygen atom has a partial positive charge on it.
Factors that determine the polarity of a molecule
The polar molecule always has a net dipole moment value. For example, the dipole moment of ozone is 0.53 D. Debye is the SI unit of dipole moment denoted by ‘D’.
The net dipole moment of a nonpolar molecule comes out to be 0 D. Greater the net dipole moment value, more is the polarity of the molecule.
In a molecule, if there is a difference in electronegativities of both atoms then the bond shared by both is polar. Greater the difference in electronegativities of atoms more is the overall polarity.
If we look at the structure of an Oxygen molecule, both oxygen atoms have the same electronegativity. Thus, O2 is nonpolar.
The polarity and non-polarity of a molecule can also be determined by just viewing the structural geometry of a molecule. If the molecule does not have symmetry, it comes out to be a polar molecule and if the shape is symmetrical, it is nonpolar.
If we look at the Carbon dioxide gas molecule, the C-O bond is polar due to the difference in electronegativity. CO2 molecule being symmetrical have both C-O bonds at 180 degrees that cancel out the polarity. Thus, CO2 is nonpolar.
By looking at these factors, we can check whether a molecule is polar or nonpolar.
Properties of Ozone
Ozone protects the earth from the ultraviolet rays coming from the sun. A layer is formed around the atmosphere spectrum and it strongly absorbs the UV rays around 220-290 nm.
Without this layer, these UV rays can damage aquatic life and plants on the earth’s surface and humans too. However, the Ozone layer is getting depleted due to global warming increasing day by day.
Ozone is denser than the air in the environment. Its vapor density is around 24.
On liquidation of ozone, it changes to a deep blue colored liquid.
Pure ozone exists in a gaseous form of blue color with a heavy irritating odor. On solidification, it exists as violet-black crystals.
The boiling point of Ozone is around -112 degrees Celcius.
Ozone is soluble in the water at the atmospheric pressure. Thus, ozone is a good oxidizer with an oxidation potential of 2.07 V. Being a strong oxidizer, it is also used in water treatment.
Ozone is electrophilic and reacts very selectively with other elements.
Ozone is lesser stable in water than in air. In water, Ozone’s half-life rests to about 20 minutes whereas, in air, it’s half-life rests to 12 hours.
In water treatment, it is used for sterilization of drinking water because of its oxidizing property.
It is also used in textile industries for bleaching purposes.
So, I hope you understood why Ozone is polar in nature and what are its characteristics.