Difference Between Isotopes and Isobars and Isotones

Key Difference – Isotopes vs Isobars vs Isotones
 

Isotopes are atoms of the same chemical element having different numbers of neutrons. Therefore isotopes of the same chemical element have the same atomic number but different atomic masses. Isobars are atoms of different chemical elements. Therefore the atomic numbers are essentially different from each other. Isotones have the same number of neutrons in their atomic nucleus. The key difference between isotopes, isobars and isotones is that isotopes are atoms with the same number of protons, but differing numbers of neutrons and isobars are atoms of different chemical elements having equal values for atomic mass whereas isotones are atoms of different chemical elements having an equal number of neutrons in the atomic nucleus.

CONTENTS

1. Overview and Key Difference
2. What are Isotopes
3. What are Isobars
4. What are Isotones
5. Side by Side Comparison – Isotopes vs Isobars vs Isotones in Tabular Form
6. Summary

What are Isotopes?

Isotopes are atoms with the same number of protons, but differing numbers of neutrons. A number of protons in the atom is the atomic number of that atom. A particular chemical element has a fixed number of protons. Hence, the atomic number of the atoms of the same chemical element is similar to each other. Therefore, isotopes are atoms of the same chemical element. The total number of protons and neutrons is known as the atomic mass. Isotopes have different atomic masses.

The chemical behaviour of isotopes of a chemical element is identical, but the physical properties are different from each other. Almost all the chemical elements have isotopes. There are 275 known isotopes of 81 stable chemical elements. For a particular chemical element, there are stable isotopes as well as radioactive isotopes (unstable).

An isotope is named using the name of the chemical element and the atomic mass of the isotope. For example, the two isotopes of Helium are noted as “helium-2” and “helium-4”. Some examples of isotopes are given below.

What are Isobars?

Isobars are atoms of different chemical elements having equal values for atomic mass. Atomic mass is the sum of protons and neutrons in the nucleus of an atom. A proton or a neutron is known as a nucleon. Therefore, isobars have the same number of nucleons.

The atomic numbers of these isobars are different from each other because different chemical elements have different atomic numbers. The Mattauch isobar rule states that if two adjacent elements on the periodic table have isotopes of the same mass number (isobars), one of these isotopes must be radioactive. If there are isobars of three sequential elements exist, first and last isobars are stable, and the middle one may undergo radioactive decay. An isobar series is a collection of different isotopes that have the same atomic mass.

What are Isotones?

Isotones are atoms of different elements having an equal number of neutrons in the atomic nucleus. Isotones have different atomic numbers (number of protons in the nucleus is different from each other) as well as different atomic masses. It can be expressed as below;

Atomic number = Z

Atomic mass = A

Number of neutron = N

For all isotones in one series, A≠Z but (A-Z)=N (N is equal for all the isotones in one series). Some examples for isotones are given below.

What is the Difference Between Isotopes and Isobars and Isotones?

Summary – Isotopes vs Isobars vs Isotones

Isotopes, isobars and isotones are terms used to describe relationships between atoms of different chemical elements. The difference between isotopes, isobars and isotones is that isotopes are atoms with the same number of protons, but differing numbers of neutrons and isobars are atoms of different chemical elements having equal values for atomic mass whereas isotones are atoms of different elements having an equal number of neutrons in the atomic nucleus.

Reference:

1.Helmenstine, Anne Marie, D. “Isotopes Definition and Examples in Chemistry.” ThoughtCo, Aug. 4 2017. Available here
2.The Editors of Encyclopædia Britannica. “Isotone.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 20 July 1998. Available here  
3.“Isobar (Nuclide).” Wikipedia, Wikimedia Foundation, 27 Dec. 2017. Available here 
4.Herzog, Gregory F. “Isotope.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 6 Dec. 2017. Available here 

Image Courtesy:

1.’Izotopii hidrogenului’By Nicolae Coman – Own work, (CC BY-SA 3.0) via Commons Wikimedia