• When two or more atoms have the same number of protons but different numbers of neutrons, they are known as isotopes.  For example – Hydrogen (H₁), Deuterium (H2), and Tritium (H3).
• They have the same atomic number and fall at the same place in the periodic table. 
• Isotopes have nearly identical chemical behavior but different physical properties and atomic masses. 
• Almost every chemical element has one or more isotopes. 

History of Isotopes

In the early 1900s, J.J.Thomson with the help of his student Francis W. Aston identified two different types of Neon atoms – one with 10 electrons, 10 protons, and 10 neutrons and the other with 10 electrons, 10 protons but 12 neutrons. Aston later invented the Mass Spectrograph, which was used to identify hundreds of other isotopes of different elements. Aston was awarded the Nobel Prize in Chemistry in 1922 for his work. 

Properties of Isotopes

• The chemical properties of distinct isotopes of an element are the same. This is because electrons and protons define the chemical properties. Since the only difference in isotopes of an element is the different number of protons, the chemical properties remain the same.
• The physical properties of different isotopes of an element are different. This is because the physical properties of an element depend on the element’s atomic mass, which is made up of protons, electrons, and neutrons. Since different isotopes of an element have different masses, their physical properties differ.   
• Some isotopes are unstable. Each nucleus contains a certain number of neutrons that make it stable. However, it may also contain some extra neutrons. If the nucleus becomes large enough due to the presence of neutrons, it will become unstable and will try to lose some neutrons or protons to achieve stability. 

How can the total number of neutrons in the nucleus of a given isotope be determined?

The total number of neutrons in the nucleus of a given isotope can be determined using the atomic mass and the atomic number of that isotope.

• Atomic mass

Atomic Mass is the total number of protons and neutrons found inside the nucleus of an atom.  It is also called the mass number. Atomic mass is the amount of matter present inside the nucleus of an atom. 

•  Atomic number

Atomic number refers to the number of protons present inside the nucleus of an atom, irrespective of the neutrons present. 

To determine the total number of neutrons in a given isotope, we need to subtract the atomic number from the mass number. 

Examples

1. Calculate the number of neutrons present in an isotope of Potassium (K) having mass number 40 and atomic number 19;

          40 – 19 =21

This isotope has 21 neutrons.

1. Calculate the number of neutrons in carbon-16.

The atomic number of carbon is 6

Therefore, 

16 – 6 = 10

  This isotope of carbon has 10 neutrons. 

1. Calculate the number of neutrons in Zinc-65

The atomic number of Zinc is 30

Therefore, 

65 – 30 = 35

  This isotope of Zinc has 35 neutrons. 

Conclusion

Almost all the elements have isotopes. Therefore, it is crucial to learn about them. Isotopes have a lot of uses. Different isotopes of carbon are utilized differently during photosynthesis, making it a complicated process. Radioactive or unstable isotopes are used more frequently in nuclear medicine procedures, for example,  brain, thyroid, liver, bone marrow, lung, heart, and intestinal scanning, cancer detection, and treatment, especially in eyes and skin, gamma-ray irradiation of tumors, treatment of goiter, etc. They also play an essential role in our daily lives; for example, uranium isotopes are used as fuel in the nuclear reactor. Isotopes are also used to detect flaws in the steel section of the bridges, detect contraband at international borders, power batteries for space exploration, etc.