Radioactivity-Soddy-Rajan’s Displacement Law

Radioactivity is a phenomenon through which an amount of energy is produced from the spontaneous reactions of less stable nuclei. They have the characteristics such as the liberation of excess amounts of energy, and spontaneous in nature, first-order reactions. Group displacement law is given by Soddy regarding the changing positions in the modern periodic table of by-products of disintegrated elements such as alpha particle, beta particle, and gamma particle. This article also includes the alternative atomic and mass numbers of these radioactive elements during any natural radioactive decay.

Radioactivity: 

The process of radioactivity was discovered by A.H. Becquerel in 1896. It is a phenomenon in which stable atomic nuclei are formed by a spontaneous disintegration of least or less stable atomic nuclei.

Features of radioactivity reactions:

• Release of a tremendous amount of energy (exoergic).
•   Random in nature (follows spontaneity).
•   A kind of first-order process.
•   Utilisation of a small amount of mass for producing energy.

Every radioactive species is characterised by its half-life because radioactive reactions come under first-order reactions. In the process of radioactive decay, an excess amount of energy is produced, generally ten lakhs times more than the amount of energy produced during an exothermic reaction. This process is not affected by any parameters such as temperature and pressure, as it is a nuclear reaction instead of an electronic phenomenon. However, this can also be slightly altered by increasing the pressures on some radionuclides. Radioactive (unstable element) is shown by the chemical symbol of the element.

The S.I. unit of radioactivity is the Curie after the name of Marie Curie, and it is defined as the rate of integration per second (dis/sec) i.e., 3.700 × 1010 disintegrations per second. Recently, a new unit is also used to measure the radioactive reaction is the Becquerel (1bq = 1dis/sec).

Soddy- Rajan’s displacement law

Particles of radioactive isotopes are non-stable in nature. During the process of disintegration of atoms, a new element is formed. The new elements exhibit completely new properties-physical and chemical both.

The element that undergoes disintegration is the parental element and the by-product element of it is the daughter element. After an in-depth study analysis of by-products of the disintegrated elements by Soddy and Fajan, the following conclusions are given below,

Alpha emission: 

It is represented by 2He4. It is the nucleus of helium. Its atomic number is two and its atomic mass is four. Hence, after the disintegration of the alpha particle, the atomic number will be reduced by two, and atomic weight will be reduced by four.

Hence, the by-product of the disintegrated element, i.e. daughter element, has placed two groups lower in the modern periodic table.

The alpha particle emission can be represented by

ZXA  → z-2YA-4 + He

Where A is the atomic mass, and Z is the atomic number

Example, 92U238 → 90Th234  + He

Beta emission: 

It is a type of beta decay transformation of the neutron from the proton that takes place or vice versa inside the nucleus of unstable elements. These processes support the nucleus to get closer to the optimum ratio of neutron/proton. It is an electron (e) and denoted by β.

During the process of beta particle disintegration, the atomic number will be increased by 1, and atomic mass will remain the same. Hence, the by-product of the process, i.e., will place one group higher in the Modern Periodic table.

The beta-particle emission is represented by

ZXA  → z-1YA + −1β+ v

Where Z is the atomic number and A is the atomic mass and v is the basic particle known as antineutrino which does not have mass and any charge.

Example,

90Th228 → 89Ac228 + −1β+ v

Gamma emission: 

The atomic number and atomic mass both will change during the process of gamma emission. Hence, its place in the Modern Periodic table will remain the same. During any natural radioactivity of gamma emission, it does not accompany either alpha or beta emission.

Therefore, Soddy and Fajans(1911-1913) explained the displaced positions of the daughter atoms in the Modern Periodic table and their arrangements.

In the case of a particle radioactivity reaction, it is displaced to the left in the Modern periodic table because of the reduction of the atomic number by 2.

In the case of the β-particle (positron) radioactivity reaction, it is displaced to the right in the Modern periodic table because of the increased atomic number by 1.

For lanthanide series and actinide series, Group displacement law applied with care.

Conclusion

The phenomenon of the radioactivity process is very critical for our daily based lives. The process of radioactivity creates many harmful effects. They have the characteristics such as the liberation of excess amounts of energy and spontaneous, in nature, first-order reactions. Group displacement law is given by Soddy regarding the changing positions in the Modern periodic table of by-products of disintegrated elements such as alpha particle, beta particle, and gamma particle.