All elements are made up of tiny invisible particles called atoms. According to the scientists, at the centre of an atom there is a core called the nucleus around which the electrons revolve in different orbits. The nucleus is made up of two types of particles called protons and neutrons. All atoms of a particular element have the same number of protons in the nucleus. However, the number of neutrons in the nucleus can vary without changing the chemical nature of the element.
The number of protons in an atom is called its atomic number while the total number of protons and neutrons is called its mass number or atomic weight. Chemical properties of a substance depend upon the electrons outside the nucleus while the physical properties on its mass number. Atoms of the same element having the same atomic number but different mass numbers are called its isotopes. For example, hydrogen has three isotopes – protium, deuterium and tritium. Protium has only one proton, deuterium or heavy hydrogen has one proton and one neutron while tritium has one proton and two neutrons. Tritium does not exist naturally. It is produced by artificial means.
All the isotopes of the same element have the same chemical properties but different physical properties. Almost all elements are mixtures of isotopes. Oxygen and chlorine have two isotopes each.
Isotopes of some elements are radioactive in nature, i.e. they emit invisible radiations and decay into isotopes of other elements. Isotopes of an element are separated by an instrument called mass spectograph. Particle accelerators are used to prepare ‘radio isotopes’.
Radio isotopes are very useful. Cobalt-60 and Radium isotopes are used to burn out cancerous growths. Carbon-14 is used to determine the age of the dead plants and animals. This process is called radioactive dating. Isotopes of iodine are used for the treatment of goitre. Artificial radio-isotopes are used to study the chemical reactions. They are also used as tracers to study the movements of compounds in plants and animals. With the help of isotopes many diseases are diagnosed. This branch of medicine is called nuclear medicine.
Manufacturers of precision instruments use some isotopes to detect tiny flaws in metal castings and to make extremely fine measurements.
