Ozone is a form of oxygen in which each molecule contains three atoms of oxygen instead of the usual two. Its chemical formula is 
and the three atoms are arranged in a triangular shape. This means that although its molecules contain only oxygen atoms, their number and arrangement differ from that of oxygen gas.
Ozone is light blue in colour and has a strong odour. The characteristic smell can be experienced near running electric motors. It is poisonous in nature, differing considerably from oxygen in its chemical properties. It is found in the atmosphere in very small quantities, the highest concentration being at high altitudes where it is formed by the reaction of ultraviolet rays on oxygen.
To obtain ozone, ordinary oxygen is passed through a tube where it is subjected to a silent electrical discharge. The electrodes are covered with insulating materials (glass or mica) so that the discharge currents are kept low, and high voltage pulses are supplied between the electrodes. This method has to be used so that oxygen acquires the energy it needs to form ozone but at the same time ozone does not become so hot that the molecules again break up into ordinary oxygen.
Ozone is a powerful oxidizing agent. It is used to sterilize water, to purify air, to decolourize foods, and act as bleach. Its ozonide-forming property is used in several industrial processes in the manufacture of drugs and plasticizing materials.
An ozone layer in the atmosphere absorbs much of the sun’s harmful ultraviolet rays and consequently saves the animal and plant lives on Earth. This is due to the fact that the ultraviolet rays spoil the vegetation and cause diseases like cataract and skin cancer. Recently the discovery of holes in the ozone layer created a great concern and hence the use of substances like chlorofluorocarbon (CFC), which are responsible for the depletion of the ozone layer, is being gradually eliminated.