J.J. Thomson proposed the model of an atom in 1903, which played a crucial role in understanding the existence of electrons and protons. Here is a detailed explanation of his model and its significance:

The Plum Pudding Model:
J.J. Thomson's atomic model, also known as the Plum Pudding Model, suggested that an atom consists of a positively charged sphere with negatively charged electrons embedded within it, much like plums in a pudding.

Key Points of the Plum Pudding Model:
- According to Thomson, an atom is composed of a positively charged substance with negatively charged electrons scattered throughout it.
- He proposed that the positive charge and negative charge within an atom are evenly distributed, resulting in overall neutrality.
- The negatively charged electrons are held within the atom by the electrostatic force of attraction between the positive and negative charges.

Significance of J.J. Thomson's Model:
- Identification of Electrons: Thomson's model provided the first evidence of the existence of electrons within an atom. He conducted the cathode ray tube experiment, where he observed that cathode rays (streams of electrons) were deflected by electric fields. This led him to conclude that electrons are negatively charged particles present in atoms.
- Understanding Atomic Structure: Thomson's model challenged the earlier belief that atoms were indivisible. It suggested that atoms contain smaller particles, known as electrons, and that the atom itself is composed of a combination of positive and negative charges.
- Basis for Future Discoveries: Thomson's model laid the groundwork for further exploration of atomic structure and paved the way for the subsequent experiments conducted by Ernest Rutherford, which eventually led to the discovery of the atomic nucleus and the understanding of the atom's planetary model.

In conclusion, J.J. Thomson's proposal of the Plum Pudding Model in 1903 was a significant contribution to the understanding of atomic structure. His model introduced the concept of electrons and their presence within atoms, which played a crucial role in the development of modern atomic theory.