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What are Isotopes?

  • Last Updated : 21 Jul, 2021
Geek Week

In Structure of Atom, we saw different types of atomic models like Thomson’s model, Rutherford’s Model, etc. and from there we get the understanding of terms atomic mass and number. In nature scientists have found several elements which have the same atomic mass or same atomic number, so to have a clear understanding of these elements, they are divided into several categories named Isotopes, Isobars, Isotone, etc.


Consider two objects that have the same color and have the same physical look, and you cannot tell them apart. However, when the weights of these two items are compared, they are found to be different. This example might help you understand the idea of isotopes.

Atoms, as we all know, are made up of electrons, protons, and neutrons. The nucleus is made up of protons and neutrons, while electrons orbit around it. Atomic mass is the sum of a number of protons and neutrons, while atomic number is equal to the number of protons. The number of protons in an element is constant, while the number of neutrons varies. 

Isotopes are atoms in which the number of neutrons varies but the number of protons remains constant. Based on the definitions of atomic mass and atomic number provided above, we may deduce that isotopes are elements that have the same atomic number but a different mass number. 

Or in other words, elements that have the same number of protons, but different numbers of neutrons are called Isotopes. e.g. 1H1 (Protium), 2H1 (Deutetrium), 3H1 (Tritium) are isotopes of Hydrogen.

Applications of Radioactive Isotopes

Radioactive isotopes have several applications. Generally, however, they are useful because either we can detect their radioactivity or we can use the energy they release. They are frequently used in medicines, industry and agriculture for variety of useful purposes. The main role of Radioisotopes is that they are used as Tracers

Tracers are chemical compounds in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay, they are used to trace the path of radioisotope and thus have several uses.

Following are the applications of Radioactive Isotopes:

  1. Radioactive Dating: Radiocarbon dating, which determines the age of carbon-bearing objects, use the radioactive isotope carbon-14. Because radioactive isotopes’ half-lives are unaffected by external variables, the isotope functions as an internal clock.
  2. Irradiation of Food: Some radioactive compounds produce radiation that may be used to destroy germs on a range of goods, therefore prolonging their shelf life. Tomatoes, mushrooms, sprouts, and berries are all irradiated with cobalt-60 or cesium-137 emissions.
  3. Medical Applications: Radioactive isotopes offer a wide range of medicinal uses, including the diagnosis and treatment of sickness and disease. For example, 32P is utilized for cancer identification and therapy, particularly in the eyes and skin, 59Fe for anemia diagnosis, 60Co for tumor gamma ray irradiation, 131I for thyroid function diagnosis and treatment, and many more uses.
  4. Other uses: Radioactive isotopes find uses in agriculture, food industry, pest control, archeology and medicine. 


Isobars are elements that have different chemical properties but the same physical properties. As a result, isobars are elements that have a distinct atomic number but the same mass number. Their chemical properties differ due to the variation in the amount of electrons. It has the same atomic mass as the other but a different atomic number. Because an increased number of neutrons compensates for the difference in nucleon count.

Elements that have the same mass number or one can say same atomic mass are known as Isobars. e.g. 40Ar18 (Argon) and 40Ca20 (Calcium) are examples of Isobars as they have same mass number (i.e. 40).

Example of Isobar

Applications of Radioactive Isobars

  1. An isobar of Cobalt is used to treat cancer
  2. An isobar of Phosphorus is used to treat blood cancer
  3. Iodine is used to treat thyroid disorders
  4. Isobars are used to treat tumors, blood clots etc. 
  5. Also, they can be used in meteorology and weather maps.

Problems Based on Isotopes and Isobars

Problem 1: Differentiate between Isotopes and Isobars?


Following are the differences between Isotopes and Isobars-





Isotopes are atoms with the same number of protons but differ in numbers of neutrons.Isobars are atoms of different chemical elements having equal values for atomic mass


Isotopes of an element have the same chemical propertiesIsobars differ in their chemical properties


Isotopes occur in the same place in the periodic table.Isobars occur at a different place in the periodic table.


Isotopes have different physical properties from each otherIsobars mostly have similar physical properties.


Similar arrangement and number of electronsArrangement of electrons are different.


They are atoms of the same element. They are atoms of different elements.

Problem 2: Isotopes have the same chemical properties while isobars do no have the same. Why?


Isotopes of an element have the same number of electrons and protons but have the different numbers of neutrons. Since the chemical properties of elements depend upon the atomic number, isotopes of an element have simile chemical properties.

On the other hand, isobars have the different numbers of electrons, protons as well as neutrons.

Thus, isobars have different chemical properties.

Problem 3: The number of protons and electrons is the same in an atom, then why is it wrong to say that the atomic number of an atom is equal to its number of electron?


It is right to say that the atomic number of an atom is equal to no. of electrons in that atom, but it is correct only for the neutral atom which means the atom having neither positive nor negative charge. If there is an ion in which either no of electrons are less or more than electron then we cannot say that atomic number is equal to the number of electrons.

Problem 4: What is the main difference between radioactive isotope and simply the term isotope?


An Isotope is an atom of an element with a different number of neutrons than the original element. e.g. Carbon usually has 6 neutrons. An Isotope of carbon would be carbon 13. This atom is an isotope because it has 7 neutrons instead of 6.

However, Radioisotope is also an isotope by nature. The difference is that radioisotopes are very unstable and contain high levels of nuclear energy and emit this energy in the form of nuclear radiation. The main difference: Isotopes can be stable or unstable, but Radioisotopes are always unstable.

Problem 5: How are radioactive isotopes produced?


There are several sources of radioactive isotopes. Some radioactive isotopes are present as terrestrial radiation. Radioactive isotopes of radium, thorium, and uranium, for example, are found naturally in rocks and soil. Uranium and thorium also occur in trace amounts in water. Radon, generated by the radioactive decay of radium, is present in the air. 

Organic materials typically contain small amounts of radioactive carbon and potassium. Cosmic radiation from the Sun and other stars is a source of background radiation on Earth. Other radioactive isotopes are produced by humans via nuclear reactions, which result in unstable combinations of neutrons and protons. One way of artificially inducing nuclear transmutation is by bombarding stable isotopes with alpha particles.

Problem 6: Which isotopes are used in cancer treatment and why?


Yttrium-90 is used for the treatment of cancer, particularly non-Hodgkin’s lymphoma and liver cancer, and it is being used more widely, including for arthritis treatment. Lu-177 and Y-90 are becoming the main RNT agents.

A large dose of radiation caused reddening of the skin, damage to tissues, radiation necrosis, sterility. Small animals could be killed. Such damage to growing matter suggested that cancer might be treated by the new radiation. Little was known about the cause or mechanism of cancer, but its manifestation as an uncontrollable “growth” was easy to see, and surgeons treated cancer by cutting away the diseased part. Could radiation replace surgery? The experiment showed that apparently, it could. Not only did radiation inhibit the growth of these malignant cells, but it seemed to be more effective against them than against normal body tissues. On this last fortunate fact depends on the successful treatment of cancer by radiation. It is the basis for radiotherapy, the new medical discipline that grew out of Roentgen’s discovery.  

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