# Composition and size of Isobars

Alfred Walter Steward is the person who for the very first time introduced the term of Isobars. The term has a Greek origin and is composed of two separate words. The first section of the word is “Isos” which means “Equal”, while the second “Baros” means the “Weight”.

## What are Isobars?

Nuclides of atoms that have a similar number of nucleons are known as the Isobars. The characteristic of isobars is that they have the same number of protons in their nucleus (or same atomic number), but the mass number is always different. The prominent examples of isobars include argon, potassium, chlorine, and Sulphur. When you will look carefully into these examples and their protons, neutrons, and electrons, you will come to know that all of them have forty nucleons in their nuclei, while the number of protons and neutrons are different.

## Mass of Isobars

When we talk about the same mass of the Isobars, that does not essentially mean that the corresponding nucleus has the same mass or the atomic mass is something that is pointed out here. We all know that the mass number is just the same as the number of neutrons and the atomic number.

According to Seersucker’s formula, the mass number relates to the atomic number and the number of neutrons in a non-linear form. This means that even for the constant mass number, the relationship will remain the same. So, you should be very clear about this concept, and never confuse that the relationship is linear as they share a direct conversion with each other.

## Stability of Isobars

According to the Mataucha isobar rule, the periodic table has elements that are aligned adjacent to each other. In both of them, the mass number is the same which means that they are isobars. This rule claims that either one of them is radionuclide or you can simply say that one of them is radioactive. Also, in some cases, three elements in the sequence are isobars, so the first one and the last one will remain stable, while the middle one will undergo branched decay. As a result of this branched decay of the middle element, the daughter isobars are generated. It is to be kept in mind that in the case of isobars, no sequential elements can be stable isobars. This piece of information is of the most important in the case of isobars.