Difference Between Isotopes and Isobars

Isotopes vs Isobars
 

Atoms are the small building blocks of all existing substances. There are variations between different atoms. Also, there are variations within the same elements. Isotopes are examples for differences within a single element. Isobars are different elements with a similarity.

Isotopes

Atoms of the same element can be different. These different atoms of the same element are called isotopes. They are different from each other by having a different number of neutrons. Since the neutron number is different, their mass number also differs. However, the isotopes of the same element have the same number of protons and neutrons. Different isotopes present in varying quantities, and this is given as a percentage value called relative abundance. For example, hydrogen has three isotopes as protium, deuterium and tritium. Their number of neutrons and relative abundances are as follows.

¹H – no neutrons, relative abundance is 99.985%

²H- one neutron, relative abundance is 0.015%

³H- two neutrons, relative abundance is 0%

The number of neutrons a nucleus can hold differs from element to element. Among these isotopes, only some are stable. For instance, oxygen has three stable isotopes, and tin has ten stable isotopes. Most of the time simple elements have the same neutron number as the proton number but, in the heavy elements, more neutrons are there than the protons. The number of neutrons is important to balance the stability of the nuclei. When the nuclei are too heavy, they become unstable and, therefore, those isotopes are becoming radioactive. For example, ²³⁸ U emits radiation and decays to much smaller nuclei. Isotopes may have different properties because of their different masses. For example, they may have different spins, thus their NMR spectra differs. However, their electron number is similar giving rise to a similar chemical behavior.

A mass spectrometer can be used to get information about isotopes. It gives the number of isotopes which an element has, their relative abundances and masses.

Isobars

Isobars are atoms of different elements with the same mass number but their atomic numbers are different. In other words, they have different number of protons. For example, ⁴⁰S, ⁴⁰Cl, ⁴⁰Ar, ⁴⁰K, and ⁴⁰Ca have the same mass number as 40. However, as you know atomic number of sulfur is 16, chlorine – 17, argon – 18, potassium – 19 and calcium – 20. Mass number is the total number of protons and neutrons the atoms has. Since the above atoms have different number of protons, to get the same mass number they should have different neutrons. For example, sulfur should have 24 neutrons and chlorine should have 23 neutrons. Mass number is also known as nucleons. Therefore, we can define isobars as atoms of different elements with the same nucleons.