Thomson Plum Pudding Model (1911)

“Thomson's Plum Pudding Model” is given by the English Physicist “Sir Joseph John ‘J.J.’ Thomson”. He discovered the electron (first subatomic particle) in the year of 1897. At the time of discovery J.J. Thomson called this negatively charged particle as “corpuscles”.

“Thomson's Plum Pudding Model” is first model to represent the atomic structure of matter. According to “Thomson's Plum Pudding Model”, a substance is consists of small spheres which are having the radius of about 10-10 m in diameter. The positive charge is spread uniformly though out the volume of sphere called “pudding”. The negatively charged particles ‘Electrons’ called “Plums” are distributed as point charges in shells as shown in figure below- The positively charged sphere excerpts the force on negatively charged electrons. The direction of net force on negatively charged electrons due to positively charged sphere is towards the center of the sphere. These negatively charged electrons repel to each other & form the shells. Thomson's Plum Pudding Model hold sway for few years until the Ernest Rutherford announced the nuclear model of atom in the year of 1911. After Ernest Rutherford’s nuclear model of atom in 1911, the interest in Thomson's Plum Pudding Model fell off rapidly. But the Thomson's Plum Pudding Model assumed its place in history as the first modern attempt to construct a theory of atomic structure.

The “Thomson's Plum Pudding Model” was given up as it failed to explain the existence of some observed phenomena. This model failed to explain the emission of electron spectrum consists of different frequencies from Thomson’s atom when it is subjected to external frequencies emitted from other substances. It also failed to explain the existence of light spectrum. For example takes the emission of light from hydrogen atom having single electron. According to Thomson's Plum Pudding Model, it can emit the light at single frequency whereas, practically it emits the light spectrum which consists of different frequencies. Due to failure of Thomson's Plum Pudding Model for explaining the above phenomenon, this model got rejected.

Even though, the Thomson's Plum Pudding Model represents a considerable progress towards the truth of matter but it failed to explain these facts. More ever, it fails to provide the satisfactory mechanism to explain the deflection of α – particle. In the year of 1911, British Physicist Ernest Rutherford gave atomic model which is capable to explain the above phenomenon such as hydrogen spectrum consisting of different frequencies, light spectrum consisting of different frequencies, deflation of α – particles in external field. Therefore the Ernest Rutherford’s nuclear model of atom in 1911 replaced the Thomson's Plum Pudding Model.