An atom is considered the basic building block of matter that possesses all the chemical properties of an element. Each atom has a positively charged nucleus at the center that contains two types of subatomic particles firmly packed together. These particles are known as protons which have a positive charge and neutral neutrons. The nucleus is surrounded by electrons that are continuously revolving in the fixed orbits around it. The atoms of each element have the same numbers of protons and electrons but, typically, not neutrons, whose numbers can vary. Isotopes are two or more types of atoms with the same number of protons but different numbers of neutrons in their nucleus. In this article, we will talk about isotopes, how they occur, stable isotopes, unstable isotopes, etc.

Isotopes can be defined as variants of chemical elements that have the same atomic numbers, but they differ in mass numbers due to different numbers of neutrons in their nuclei. The term isotope originated from the Greek word “isos” meaning “the same place.” The reason behind “the same place” is that the different isotopes of a single atom occupy the same position in the periodic table. All isotopes of a given chemical element share almost the same chemical properties but different physical properties.  For example, there are three naturally occurring isotopes of carbon which are carbon-12, carbon-13, and carbon-14.  Carbon-12 contains 6 neutrons, carbon-13 contains 7 neutrons, and carbon-14 contains 8 neutrons in its nucleus. Another common example includes the isotopes of hydrogen. Hydrogen is the only element whose isotopes are known by unique names that are represented by the figure below:

Notation 

Isotopes are written in two different ways.

It is generally referred to as the percentage in which the isotopes of a chemical element can be found in nature. It is also known as relative abundance. These ratios play an important role in calculating the atomic mass of an element. 

The total number of neutrons can be determined by subtracting the atomic number of the element from the mass number of the isotope. For example, the oxygen-16 isotope of oxygen has a mass number of 16. The atomic number of oxygen is 8. Thus, the total number of neutrons in the oxygen-16 isotope is equal to 8.

This includes two major types of isotopes, which are stable and unstable. This distinction is specifically dependent on the stability or instability of the nuclei of these isotopes. 

Stable isotopes are known to have stable nuclei that do not decay. In other words, stable isotopes have extremely long half-lives. The half-life is around in the order of hundreds of millions of years. They are typically non-radioactive forms of atoms. Although stable isotopes do not emit radiation, their unique properties enable them to be used in a wide range of applications such as environmental studies, water, and soil management, etc. Common examples of stable isotopes include carbon-12, carbon-13, oxygen-16, oxygen-17, and oxygen-18.

If an element has only one stable isotope, that element is known as a monoisotopic element. Iodine is an example of a monoisotopic element.

Some isotopes have unstable nuclei. These isotopes are radioactive. Therefore, they are known as radioactive isotopes. For example, uranium-235, uranium-238, chlorine-36, tritium and carbon-14 are radioactive isotopes. 

Summary