CBSE Class 11-science Answered

Ozone is an unstable blue gas having pungent odour. Chemically, it is an allotrope of Oxygen which is an element in the gaseous form. It has three oxygen atoms in its single molecule and in the language of Chemistry; its molecular formula is 03. It is used as a powerful oxidant, bleach, and water purifier. It is also used to treat industrial wastes.

 

If found in the troposphere; ozone acts as a powerful pollutant. But, when found in the stratosphere, it acts like a friend of the earth because it shields most of the ultra violet radiations and does not allow them to pass on towards the same. In stratosphere, it is found in the form of a dense layer called as the Ozone Layer or the Ozone Belt. Thus, the Ozone Belt in the stratosphere acts like a Protective Umbrella of the earth. Let us see, how this gas is formed in the atmosphere.

 

Ozone is formed in the stratosphere when oxygen molecules Photo dissociate after absorbing an UV Photon of shorter wavelength(less than 240 nm) to produce two oxygen atoms. Ozone is mainly produced from oxygen containing molecules such as Sulphur dioxide, Nitrogen Oxides, etc. also when these molecules are exposed to ultraviolet radiations. In Chemistry, a molecule is the particle of any substance that can remain in a free state. But, what is an atom? Well, an atom is the smallest particle of a substance that can not usually remain in a free condition. Two or more atoms combine to form a molecule. Through the foregoing lines, we came across another term, allotrope. One of the two or more different forms of molecules of an element is called as an allotrope.

A large number of ozone molecules assemble around the earth to form the Ozone Layer which extends from 13 to 48 km above the earth surface. On an average, it is about 230 Dobson units (DU) in thickness. DU is the unit which measures thickness of the ozone layer. It equals to 0.01 mm.