[Physics Class Notes] on Neutrons, Isotopes, Isotones and Isobars Pdf for Exam

A neutron is a subatomic particle holding no charge. This particle was discovered by James Chadwick in 1932 where he observed that when beryllium was bombarded with the alpha particles neutral radiation was emitted. The application of principles of conservation of energy and momentum stated that the bombardment of beryllium with alpha particles led to extremely penetrating radiations that could not be deflected by an electrical or magnetic field were not protons. They were neutrons because neutrons are chargeless particles, and do not get deflected by an electric or magnetic field.

 

Moreover, after the discovery of the neutron by James Chadwick, the English physicist, several investigators in the entire world began to study the interactions and properties of the particle. Besides, it was also discovered that when elements are bombarded by neutrons, they undergo fission which is a nuclear reaction that happens when the nucleus of any heavy element splits into two equal but smaller fragments.

 

In the year 1942, under the leadership and guidance of physicist Enrico Fermi, a group of researchers showed that to sustain a chain reaction, free neutrons are made during the fission process. This major development led to the formation of the atomic bomb. Nevertheless, neutrons have become an important instrument for pure research purposes.

 

 

The Neutrons Have Slightly Higher Mass than the Protons Given by,

 

Isodiaphers 

In nuclear physics, isodiaphers refer to the set of elements having different numbers of protons (atomic number) and neutrons and mass number (no of neutrons + no of protons) however they have the same difference between the number of neutrons and protons and neutrons excess are same.

To determine if the atoms are isodiaphers, we use the formula,

 

Where P is the number of protons and N is the number of neutrons that can be calculated by the difference in mass number (A) of an atom and the number of protons in that atom. 

If the difference of N- P in each atom comes out to be the same, then those two atoms are considered as isodiaphers.

 

Isobars and Isotones

Isobars

The set of elements has the same number of nucleons, where nucleons are protons or neutrons. For example, 40 Sulfur, 40 Chlorine, 40 Argon, 40 Potassium, and 40 Calcium are all isobars. Moreover, despite having the same mass number, isobars have different atomic numbers for different chemical elements. While stable isotopes can exist in a free state, radioactive isotopes are way too unstable to even sustain. Besides, in 1918, Alfred Walter Stewart, recommended the word isobar while it is derived from the word isos, which means equal, and baros, which means weight in the Greek language.

 

Isotones

The two or more atoms or nuclei having the same number of neutrons are called isotones. For example, 36S, 37Cl, 38Ar, 39K and 40 Ca nuclei are isotones as they all comprise 20 neutrons. 

 

Isotones Examples

Example 1

Chlorine-37 and Potassium-39

Chlorine (Cl)

No of protons  = 17

No of neutrons = 37 – 17 = 20

Potassium (K)

No of protons = 19

No of neutrons = 39- 19 = 20

Cl and K are isotones

 

Example 2

32 Ge 76 and 34 Se 78

Germanium (Ge)

No of neutrons = 76 – 32 = 44

Selenium (Se) 

No of neutrons = 78 – 34 = 44

Ge and Se are isotones.

 

Isodiaphers Examples

The atoms of different elements have the same difference of neutrons and protons.

Example1

Thorium – 234  =  90 Th 144

No of protons (atomic number Z ) = 90

Since mass number = no of neutrons + no of protons

Mass number (denoted by A) = 234 and no of protons = 90

No of neutrons = 234 – 90 = 144

Difference between neutrons and protons  = 144 -90 = 54…(1)

and Uranium-238  =  92 U 238

No of protons (atomic number Z)  = 92

No of neutrons = 146

Difference between neutrons and protons  = 146 – 92 = 54….(2)

As you can see in eq(1) and eq(2) the difference between the neutrons and protons for Thorium-234 and Uranium-238 are the same. Hence we can say that these two elements are isodiaphers.

 

Example 2

9 F 19 and Sodium 11 Na 23

Fluorine  

No of protons = 9 

and number of neutrons = 10 (19 – 9)

Difference  = 10 -9 = 1

Sodium 

No of protons = 11  and

number of neutrons = 12 (23 – 11)

So the difference will be  = 12  – 11  = 1

Here, we can see that the difference is the same, i.e. 1.

Hence fluorine and sodium are isodiaphers.

 

Isomer and Isotope

Isomer

Isomer is a Greek word, which means having equal share or part.

In nuclear physics, any two or more nuclei that possess the same number of neutrons and protons and mass number, however, exist in different energy states and have different radioactive properties.

It can also be said that the nuclei exist in any of several energy states for a measurable period of time.

For example, two nuclear isomers of Cobalt-58 are 58Co and 58mCo

Where 58Co  is a lower energy isomer has a half-life of 71 days and the high energy isomer is 58mCo (here m is for metastable which means 58mCo tends to remain in the state of equilibrium) having a half-life of 9 hours undergoes gamma decay further to form 58Co.

 

Gamma Decay

It is the stage that occurs when a nucleus is in an excited state and has too much energy to be stable, only energy is emitted however the number of protons remains the same.

 

Half-life 

In radioactive decay, the half-life is the duration of time following which there is a 50% chance that the atom will undergo nuclear decay.

 

Isotope

Isotopes are the set of atoms or nuclei that have the same number of protons however different numbers of neutrons. For example, Carbon-12 and Carbon-14 have 6 protons in each, however, have 6 and 8 neutrons respectively.

 

Nevertheless, you may have never noticed but in the periodic table, each square on it represents a family none other than isotopes, in which atoms have different masses but share the same chemical properties and name. In order to understand and go in-depth to know what isotopes can be used for, one must take a peek into the interior of an atom. Besides, in nature, there are around three isotopes of carbon consisting of carbon-12, carbon-14
, and carbon-13 while all these three carbons have six protons but their neutron numbers differ. All these three are chemically indistinguishable as in each of three isotopes, the number of electrons remains the same. So if we speak chemically, different isotopes of the very same element remain identical. But if the isotope transforms into another element then the ability of this rule changes.