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Thomson’s discovery
Soon after J.J. Thomson discovered electrons, this research and experiments carried out on a cathode ray tube took place in 1897. But at this time, the nucleus was not yet discovered. This model was the first atomic model that came into existence and was published by the leading British science journal of the day named Philosophical Magazine in March 1904. This model of the atom was proposed by J.J. Thomson. He described the atom as a sphere and also proposed that the positive and negative charged species in the atom were in equal number, so therefore the atom is electrically neutral in the state.
Electron was the term coined by G.J. Stoney for the “fundamental unit quantity of electricity” in 1891. But at the time when Thomson gave his atomic model, he substituted electrons with corpuscles.
As this model was the first to get published, it attracted lots of scientists. Later, Rutherford, Bohr, Dalton, Planck, etc., came along one by one to showcase their experiments and give out the final structure of atoms that we study today.
Postulates of Thomson’s theory
The postulates that the theory of Thomson proved can be defined as the following:
Postulate 1: The atomic structure is a sphere of +ve charge, which has the corpuscles rooted in between.
Postulate 2: The +ve and the -ve charges constituting the atom are in equal amounts, which makes the atom neutral in electrical forms as a whole.
Thomson’s Atomic Model
The proposed shape was similar to a plum pudding or a watermelon and was consequently named the plum pudding model, which is fairly significant.
In the case of watermelon, the actual reddish-pink section referred to the positively charged sphere of the atom, and the seeds of watermelon present in it represented the negatively charged species known as corpuscles.
And in the case of the plum pudding model, the electrons being the plum have been submerged in the pudding, which is regarded as the positively charged sphere.
Limitations of the Thomson Atomic Model
- Thomson could not explain the force that was able to hold +ve charge and -ve charge, and this led to failure in explanation of how this stability was maintained in the atom.
- The site of the nucleus and knowledge about it was also not given by him.
- This model of the atom could not also explain the experiment of slim metal foil in which the Alpha particles were scattered by the sheet.
- No experimental support was also provided by J.J. Thomson.
Conclusion
In the end, we can conclude that the first atomic structure to be studied was given by J.J. Thomson, which had similarities to a plum pudding in structure, and it proposed the knowledge of corpuscles along with positive spheres. However, it failed to describe its stability and the existence of the nucleus. Many more reasons came along due to which it was not widely accepted.
