1. J. Thomson suggested in 1898 that an atom had a spherical structure with an evenly scattered positive charge. The electrons are immersed within it in such a way as to give the most stable electrostatic configuration. This model is known by various names, including plum pudding, raisin pudding, and watermelon. It may be seen as a positive charge pudding or watermelon with plums or seeds (electrons). The assumption that the atom’s mass is equally distributed across the atom is a vital characteristic of this model. Even though this concept may describe the atom’s general neutrality, it did not align with further research findings.

Discovery of Electron

• J.J. Thomson was the earliest to suggest an atomic structure model.
• By 1900, scientists established that the atom was a divisible particle that included a minimum of one sub-atomic component.
• The component was the electron discovered by J.J. Thomson.

Thomson’s Atomic Model

• Thomson created a model of an atom that resembled a Christmas pudding. The electrons in a positively charged sphere resembled 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.

Thomson’s Atomic Model Diagram

• Thomson’s atomic model diagram is the visual representation of the atomic model given by J.J. Thomson. The diagram depicts an atom as a spherical-shaped positive charge with a negative charge embedded in the sphere.
• This diagram resembles a Christmas pie, a watermelon, or a plum pudding.
• The plum pudding model displays electrons as negatively charged particles immersed in a sea of positively charged particles. Thomson’s atom has a structure similar to plum pudding, an English dish.
• Thomson’s atomic model is shaped like a spherical plum pudding and a watermelon. It is similar to plum pudding because the electrons in the model mimic the dried fruits contained in a positive charge sphere, precisely like a spherical plum pudding. The model was also linked to a watermelon because the red edible component of watermelon was compared to the sphere with a positive charge, and the black seeds filling the watermelon resembled the electrons inside the sphere.

Limitations of J.J. Thomson’s Atomic Model

This model was perhaps the most foundational of all the others. It had many flaws, but it piqued the interest of other scientists and opened the path for additional essential findings in the domain.

Below are the limits of J.J. Thomson’s atomic model:

• Thomson did not mention the existence of a nucleus in the atom in the model.
• It did not explain how the positive charge might contain the positively charged electrons. Thus, it couldn’t 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 bulk of these alpha particles escape via gold foil, although some are deflected through minor and significant angles. Still, others rebound fully, reverting to their original course.
• It lacked experimental data and was based solely on Thomson’s imagination.

Conclusion

Various scientists gave several atomic models as they discovered more and more about the structure of an atom. Scientist J. J. Thomson gave an atomic model that described the atom as a spherical positively charged ball with a negative charge spread across the sphere. According to J.J. Thomson’s atomic model, electrons are embedded throughout the positively charged spheres. However, research conducted by the other physicists revealed that protons are just found in the center of the atom, and electrons are scattered about it. While Thomson’s model established why atoms are electrically neutral, it did not explain the findings of other scientists’ investigations.