Isotopes: Types, Applications, Representation and Examples

Isotopes are the elements that have the same number of electrons and protons but a varying number of neutrons. In other words, they have same atomic number but different atomic mass.

• The atomic number of an element is determined by number of electrons. 
• Isotopes are categorized into three types: Stable, Primordial, and Radioactive isotopes. 
• Hydrogen is group I element which has three isotopes: Hydrogen, Deuterium, and Tritium.
• Isotopes plays an important role in nuclear reactors and treatment of cancers.

Read also: Basic Concepts in Chemistry

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What are Isotopes?

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Isotopes are defined as those nuclear species which have the same atomic number but a different mass number. The difference in mass number is due to the presence of a different number of neutrons in the elements. 

• The most common example of isotope is hydrogen which exists in three different forms: ₁H¹,₁H² ,₁H³.
• Stable isotopes are found naturally and are unreactive in nature. 
• The isotopes which are highly reactive in nature are called unstable or radioactive isotopes. For example- Uranium.

Calculating the Neutrons in an Element

The nucleus of any element comprises a set of neutrons and protons. A total number of neutrons and protons together represents the mass number of an element. 

Therefore the number of neutrons is determined by the difference between the mass number and the atomic number. For example, the mass number of tritium is 3 and the atomic number is 1.

The formula for number of neutrons is given as: 

Therefore, using the formula, number of neutrons in tritium = 3 - 1 = 2

Hence, tritium has 2 neutrons in excess as compared to protium.

Atom

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Representation of Isotopes

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For the representation of isotopes, atomic number and atomic mass of an element must be identified first. Moreover, the symbolic representation of isotopes are done by following ways:

1. First, the name of the element is written, followed by the hyphen and the mass number of the respective isotope.
2. In this method of representation, we follow the standard, ^A_ZE notation.

Representation of Isotopes

Here E represents the element, A represents the mass number, and Z represents the atomic number. The mass number A is written in superscript, and Z is written in the subscript, i.e., _Z^AE.

For example, isotopes of hydrogen protium, ₁¹H, Deuterium: ₁²H, and tritium: ₁³H.

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Types of Isotopes

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Isotopes are broadly categorized into three categories:

• Stable isotopes
• Primordial isotopes
• Radioactive isotopes

1. Stable Isotope

The Isotopes which are having extremely long half-lives (half-life is defined as the period in which the compound undergoes decomposition and attains the concentration or weight equal to half, or 50% of its initial concentration or weight), are termed as stable isotopes. Some stable isotopes are

• Carbon: Carbon-12, Carbon-13
• Oxygen: Oxygen-16, Oxygen-17, Oxygen-18

2. Primordial Isotope

These are the isotopes possessing primordial nuclei. Primordial nuclides are the ones that have existed since the formation of our solar system. There are a total of 339 naturally occurring isotopes on earth, out of these 339, 286 isotopes are primordial in nature.

3. Radioactive isotopes

Certain isotopes have very short lives and decay rapidly characterized by the emission of radioactive waves. Such isotopes are termed radioactive isotopes. Some radioactive isotopes are:

• Hydrogen: Tritium
• Carbon: Carbon-14
• Chlorine: Chlorine-36
• Uranium: Uranium-235 and Uranium-238

Examples of a few isotopes

A few naturally occurring isotopes are mentioned in the table below:

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Difference between Isotopes and Isobars

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Applications of Isotopes

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1. Isotopes provide specific properties to specific elements having the same atomic number. Hence, isotopes are used for the chemical analysis of the element.
2. Isotopes are often used to determine the rate of reaction or change in concentration of the reactants and products since they are easier to determine.
3. They are also used in analytical procedures such as mass spectrometry, Nuclear magnetic resonance, etc.
4. Isotopes of uranium are used in nuclear reactors, while isotopes of cobalt and iodine are used in cancer treatment.

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Things to Remember based on Isotopes

1. Isotopes are defined as those chemical species which have the same atomic number but a different mass number.
2. The difference in mass number is due to the presence of a different number of neutrons in the elements.
3. We can find out the number of neutrons in an element by subtracting the atomic number from its mass number.
4. There are three types of isotopes: Stable, Radioactive, and Primordial
5. Isotopes and Isobars are not the same, Isobars are defined as those chemical species which have a different atomic number but have the same mass number.