[Chemistry Class Notes] on Charge to Mass Ratio Pdf for Exam

The history of quantum mechanics and the atomic structure is dated back to the times of Democritus, who is the man that first proposed the theory that matter consists of atoms. These theories did not, however, gain much importance since it lacked the technology needed. The experiments that were conducted during the nineteenth century and the early twentieth century had revealed that just an atom by itself is not the ultimate article. However, the continuous efforts of several scientists led to the discovery of different subatomic particles such as protons, neutrons, and electrons.

 

J. J. Thomson, in the nineteenth century, had proposed the Thomson Atomic Model which discovered the electron for marking the inception of subatomic particles. After the discovery of the electron, he continued with his experiments for calculating the mass and the charge of the electron. With the help of these calculations, he made a derived formula to calculate the charge to mass ratio of electrons. In this article, we will study the mass to charge ratio and the calculation of the charge by mass ratio.

What is an Electron?

The electron is known as a negatively charged particle having relatively lower mass. As such, it is easily deflected by passing it closer to the other electrons or even the positively charged nucleus of the atom.

 

 

Charge to Mass Ratio of an Electron

The charge to mass ratio of an electron is denoted by the following formula :

[frac {e} {m}]  = 1.758820 × 10¹¹ C/kg  

 

Where in,

 

m = mass of electron in kg 

 

    = 9.10938356 × 10^-31 kilograms.

 

e  = magnitude of the charge of the electron in coulombs 

 

    = 1.602 10^-19  coulombs.

Experimental Setup to Determine the Charge to Mass Ratio of Electron

Thomson observed while carrying out the discharge tube experiment that the particles of cathode tend to deviate from their actual path. He noticed this deviation of the path in the presence of the magnetic or electric field being dependent on different related parameters. These parameters are as follows:

1. The particles having a greater magnitude of charge experienced much higher interaction with the magnetic or electric field. Hence, they possessed a higher deflection.

2. The lighter particles experienced a greater deflection when compared to the heavier ones. Hence, deflection is inversely proportional to the mass of that given particle.

3. The deviation of the particle from its actual path is directly proportional to the strength of the magnetic and the electric field that is present.

 

 

Let us understand these parameters by understanding the experimental observations.

1. The electrons underwent deviation from their path and hit the cathode-ray tube at a point x under the presence of the lone electric field. 

2. The electrons, similarly, struck the point z of the discharge tube only when the magnetic field was present.

3. Hence, for making the electrons continue on their same path, balancing the magnetic as well as the electric field that is acting on them is important. 

4. And finally, depending on the deflection of the electron, J. J. Thomson had calculated the charge to mass ratio value of the electron.

 

Just after the discovery of Electron J.J Thompson had done so many experiments in order to know and calculate the charge and mass of electrons. The article discusses the experimental setup to determine the charge-to-mass ratio of an electron.