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Nuclide Definition

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The word “Nuclide'' was coined by an American Chemist named Truman P. Kohman in 1947. The term nuclide or nuclide is taken from the word nucleus. It is one of the nuclear species.

A nuclide is like an atom or nucleus but it differs from these two. It is characterized by a number of protons and neutrons. 

In simple words, nuclide is a species of atom/nucleus. We describe it by the composition of its nucleus, by the number of protons, the number of neutrons, and the energy content.

On this page, you will learn about the nuclide, daughter nuclide, radioactive nuclide, parent nuclide, stable nuclides.

Nuclide Definition Physics

A nuclide is described by the mass number (A) and the atomic number (Z).  For considering it distinct, a nuclide must have an energy content enough for a measurable lifetime, i.e., more than 10−10 seconds. 

The term nuclide is not similar to an isotope, it is any member of a set of nuclides possessing the same atomic number but a different mass number.

For Example, Chlorine - 37 is the nucleus that comprises 17 protons and 20 neutrons, it is a different nuclide from the sodium - 23 nuclei having 11 protons and 12 neutrons, and chlorine - 35 nucleus of 17 protons and 18 neutrons.

Nuclide Symbols

Every nuclide has a chemical element symbol (E) in addition to an atomic number (Z), i.e., the number of protons with inside the nucleus, and a mass number (A), i.e., the whole number of protons and neutrons within the nucleus.

We express nuclides in the form of AXZ, where “A” is the total number of protons and neutrons, “Z” denotes the number of protons, and the difference between A and Z is the number of neutrons. 

For instance, 37Cl17

Here, Cl signifies chlorine - 37

Let’s take another example:

The symbol for the “Li” element is given as; 


Nucleon number A = total number of protons and neutrons = 7

Proton number is equal to Z = total number of protons = 3

Li = the chemical element symbol (E)

Nuclides and Radioactive Decay

Nuclides are linked with radioactive decay and they can either be stable or unstable species. 

Around 1,700 nuclides are known, of which 300 are stable and the rest radioactive. 

In 1919, a British Physicist named Francis William Aston discovered the isotopes of the light elements (light elements are hydrogen, deuterium, helium (two isotopes), lithium, and trace amounts of beryllium) at the Cavendish Laboratory, using his new invention of the mass-spectrograph. By using his newly devised invention, he also discovered more than 200 stable nuclides.

Nuclide undergoes radioactive decay is the radioactive nuclide. Now, we will understand the science behind the parent nuclide, daughter nuclide, stable nuclides with a graph in detail.

Parent Nuclide and Daughter Nuclide

A parent nuclide is a determinate nuclide. It is an isotope whose radioactive decay products are sure daughter nuclides. It is a nuclide that decays into a daughter nuclide during the process of radioactive decay. 

For example, Na-22 decays into Ne-22 after undergoing β + decay. Here, Na-22 is the parent nuclide and Ne-22 is the daughter nuclide.

Some More Examples are as Follows:

  1. Tellurium or Te-131 after undergoing β + decay forms a daughter nuclide called Iodine - 131.

Here, Iodine - 131 is the parent nuclei of Xenon - 131.

  1. Au - 208, after undergoing the nuclear reaction, produces Hg - 208.

The above examples on parent nuclide and daughter nuclide also express the relationship between these two.

You might have heard of isotopes,  the two elements having the same atomic number but a different mass number. These isotopes are clearly matching with stable nuclides; let’s understand how:

Stable Nuclides

Out of 1,700 nuclides, 300 are non-radioactive or stable.

A stable nuclide is one that never undergoes radioactive decay. When we refer to such elements, we call them stable isotopes, while the nuclides that undergo radioactive decay are called the radioactive nuclides.

The below graph shows the stable nuclide with examples of elements:

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Do You Know?

Of the recognized chemical elements, eighty elements have at least one stable nuclide. These incorporate the primary eighty-two elements from hydrogen to lead, with the 2 exceptions, technetium (element 43) and promethium (element 61), that don't have any stable nuclides. As of December 2016, there had been a complete of 253 recognized "stable" nuclides.

Examples of Isodiapheres


Thorium - 234  =  90Th144     

No of protons (Z ) = 90

Mass number (A) = no of neutrons + no of protons (Z)

Mass number = 234 and no of protons = 90

No of neutrons = A - Z = 234 - 90 = 144

Difference between neutrons and protons of Thorium  = 144 - 90 = 54…(a)

Now, for Uranium-238  =  92U238

No of protons (atomic number Z)  = 92

No of neutrons = 146

Difference between neutrons and protons of Uranium  = 146 - 92 = 54….(2)

From eq (1) and eq (2), you can see that the difference between the neutrons and protons for Thorium-234 and Uranium-238 is the same. 

Thus Th and U are examples of isodiaphers.

Example -2:

9F19  and Sodium 11Na23

For Fluorine:

No of protons = 9 

Number of neutrons = 10 (19 - 9)

Difference  = 10 - 9 = 1

For Sodium:

No of protons = 11  and

Number of neutrons = 12 (23 - 11)

So the difference is  = 12  - 11  = 1

Here, you can notice that the difference between Fluorine and Sodium is the same, i.e. 1. Hence, fluorine and sodium are examples of isodiapheres.

FAQ (Frequently Asked Questions)

Q1: Define the Atomic Nucleons.

Ans: The primary place of an atom. Atoms are composed of negatively charged electrons, definitely charged protons, and electrically impartial neutrons. The protons and neutrons (together referred to as nucleons) are positioned in a small primary place referred to as the nucleus. 

The electrons circulate in orbits that are big in contrast with the size of the nucleus itself. Protons and neutrons possess about identical masses, every kind of 1840 instances of that of an electron. The wide variety of nucleons in a nucleus is given with the aid of using the mass wide variety A and the wide variety of protons with the aid of using the atomic wide variety Z. Nuclear radii “r” are given about with the aid of using r = 1.2  x 10-15 m A1/3.

Q2: Define Stable Nuclides.

Ans: Stable nuclides are the solid isotopes of all elements. Elements with atomic quantity much less than eighty-three have as a minimum one solid isotope besides technetium (Tc, Z = 41) and promethium (Pm, Z = 61). Elements with atomic quantity among eighty-four and 92 (inclusive) are present, however a few simplest as decay merchandise of uranium or thorium.

Q3: Is Lithium a Light Element?

Ans: Yes, lithium is very light to be detected. The Li abundance can be predicted by using a machine called XRF (X-Ray Fluorescence).