Types Of Atomic Models- Failure Of Thomson’s Atomic Model

According to JJ Thomson’s atomic model, an atom is a positively charged sphere. The sphere contains equal electrons, and an atom is electrically neutral. The drawbacks of J J Thomson’s are that there is no separation between electrons and protons in this model since they are held together inside the atom, which is impossible and leads to atomic instability. However, the atom is stable. He stated that an atom is a positively charged sphere, but as we all know, a positive charge repels other positive charges, causing instability. Furthermore, the findings of other scientists’ studies and Rutherford’s alpha scattering experiment could not be explained by this concept. Later, there were advancements made to this model as well. There are five main atomic models. The types of atomic models in order are Dalton’s atomic model, Thomson’s atomic model, Rutherford’s atomic model, Bohr’s atomic model, and Schrodinger’s atomic model. 

Thomson’s Atomic Model

• Thomson created a model of an atom that resembled a Christmas pudding. The electrons in a positively charged sphere looked like raisins in round Christmas pudding.
• We may also picture an atom as a watermelon, with the positive charge scattered everywhere, such as the red edible portion of the watermelon and the electrons embedded in the positively charged spherical ball like the seeds in the watermelon.
• Thomson suggested that:
  • An atom comprises a positively charged sphere in which electrons are contained.
  • The magnitudes of the negative and positive charges are the same. As a result, the atom is electrically neutral overall.

Postulates of Thomson’s Atomic Model

• The atom is neutrally charged.
• There is a component of positive charge that cancels out electrons’ negative charge.
• This positive charge is spread equally across the atom.
• According to Thomson, negatively electrified corpuscles, or electrons, are trapped inside the homogeneous bulk of positive charge.
• Electrons may freely move throughout the atom.
• The electrons possessed stable orbits, according to Gaussian Law. If the electrons went through the positive “mass,” their internal forces were balanced by the positive charge formed naturally surrounding the orbit.
• J.J. Thomson’s atomic model was generally known as a plum pudding model because the electron distribution predicted by Thomson was comparable to the placement of plums in that dish.

Failure Of Thomson’s Atomic Model

Limitations

The following are the limitations of J.J. Thomson’s atomic model:

• Thomson’s model included no mention of the presence of a nucleus in the atom.
• It did not explain how the positive charge might contain the positively charged electrons. As a result, it could not account for the atom’s stability.
• The model could not justify the results of Rutherford’s alpha-particle scattering experiment. The model does not explain why the vast majority of these alpha particles escape through the gold foil, even though tiny and large angles deflect some. On the other hand, others recover and return to their former path.
• It was mainly based on Thomson’s imagination and lacked experimental facts.

Failure

• While the majority adopted Thomson’s model, it was rapidly rejected as it failed to realise atomic stability because it did not describe how the negative charge (electrons) is contained inside the positive sphere. In other words, it could not explain the presence of a nucleus in an atom.
• This model was the most basic of all of them. It had numerous shortcomings, but it grabbed the curiosity of other scientists and paved the way for further significant discoveries in the field.
• The model made no mention of the presence of a nucleus in the atom. It did not explain how the positive charge might contain the positively charged electrons.
• In other words, it could not account for the stability of the atom. It couldn’t account for Rutherford’s scattering experiment or the scattering of alpha particles when projected on gold foils.
• Thomson’s method was a fundamental advancement in the field of atomic chemistry. Despite significant shortcomings, it acted as a motivator for other academics in the field to investigate and reach their conclusions and interpretations.

Ahead of Thomson’s Atomic Model

After the nineteenth century, scientists faced a considerable problem in revealing the structure of the atom and explaining its crucial features. Various atomic models were offered for this purpose. After Thomson’s model failed to explain some experimental findings, Rutherford, a British physicist, experimented and developed the Rutherford Atomic Model based on the results of that experiment. Rutherford succeeded in overcoming the limitations of Thomson’s atomic model. 

Conclusion

Thompson’s concept of the atom had a massive positive core surrounded by, or possibly engulfed by, negative particles. Thompson found the negative particles that we now name electrons using cathode ray tubes. He reasoned that because atoms were electrically neutral, they must contain a positive center around which the tiny mass of electrons flowed. He was the one who discovered the electron’s mass to charge ratio. His model was termed the “plum pudding” model. Rutherford conducted an experiment in which he directed alpha particles at gold foil. He concluded that the positively charged nucleus was relatively small compared to the entire space occupied by the atom and its surrounding layers of electrons.