Thomson’s Atomic Model and Discovery of Electron

Key Concepts

• Atomic model
• J.J Thomson model of atom
• Discovery of election
• Plum pudding or watermelon model

Introduction: 

Atomic models: 

Observations and experiments mentioned by some scientists suggested that Dalton’s indivisible atom is composed of sub-atomic particles carrying positive charge and negative charge. The major problems before the scientists could recognize after the discovery of sub-atomic particles were:  

1. Stability of atom 

2. Comparing the elements behavior with both the physical and chemical properties 

3. Formation of molecules combining with identical atoms 

Explanation: 

Atomic models were proposed to explain about the charged particles in an atom.  

Two of these models, one is proposed by J.J. Thomson and the other proposed by Ernest Rutherford Bohr’s model explains how electrons revolve. 

J.J Thomson Model of atom: 

Joseph John Thomson, was a British physicist and Nobel Laureate in Physics, who studied about the electric discharge tubes, got credited for the discovery of one of the sub-atomic particles that is Electron. 

This theory was first taking place in the year 1897 and later it was proposed by J.J Thomson in the year 1900. This theory explains what exactly is present inside the atom. 

He was awarded the Nobel prize in 1906, is recognized for the experimental investigation of the conduction of electricity by gases. 

J.J Thomson’s Contribution to atom. 

• Discovery of Electron 
• Watermelon or plum pudding model 

• Cathode ray experiment 
• Isotopes 
• Mass spectroscopy 

Discovery of electron: 

Thomson was the first scientist to suggest that the fundamental or the basic unit was 1000 times smaller than that of the atom. 

What is an electron? 

Electron is one of the sub-atomic particles. Electrons, is the one which revolves around the nucleus in a circular orbit outside the nucleus.

He found that all substances used in his discharge tubes produced these particles. He even told that all atoms must even contain such particles. In other words, he explored that atom is made up of very small particles.

His model explains that, positive charge is uniformly distributed in the atom.  

The electrons are embedded in the atom so as to give a stable arrangement. He named the model, for example, plum pudding, raisin bun, or watermelon model. This model helps us to visualize as that in the pudding, positive charges are the puddings which are embedded in the negatively charged plum.

We can also think of a watermelon in which the positive charge in the atom is spread all over the watermelon’s red part, while the electrons are embedded in the positively charged sphere, like seeds in the watermelon.

Another important feature of Thomson’s atomic model is, mass of the atom is equally distributed all over the atom and he even explained the neutrality of atom, but was not stable with the earlier experiments. 

As this model is not long lived, his student Ernest Rutherford has explained the both to test the Thomson’s theory and the structure of atom. 

Summary

• 1 Joseph John Thomson, was a British physicist and Nobel Laureate in Physics, who shaded about the electric discharge tubes.

• Set is one of the sub-atomic particles. Electrons, which revolves around the mcles in a circular orbit
• He named the model for example, plum pudding, raisin bun or Watermelon model.
• He was awarded the Nobel prize in 1906, is recognized for the experimental vestigation of conduction of electricity by gases
• Positive charge in the atom is spread all over the watermelon’s red part, while the electrons are embedded in the positively charged sphere, like seeds in the