Thomson proposed in 1897 that the basic body of an atom is spherical in shape, with electrons (small particles within the atom that have a negative charge) and a positively charged “jelly” surrounding the electrons that neutralises the charge of the electrons. It was unable to explain Rutherford’s scattering experiment and the scattering of alpha particles when projected on gold foils. In other words, it couldn’t account for the atom’s stability. It did not explain how the positively charged electrons might be contained by the positive charge. The presence of a nucleus in the atom was not mentioned in the model. It had many flaws, but it piqued the interest of other scientists and paved the path for additional important discoveries in the subject.

This model was the most fundamental of all the others. Thomson’s atomic model was generally known as a plum pudding model in England because the electron distribution predicted by Thomson was comparable to the arrangement of plums in that delicacy. If the electrons moved through the positive “mass,” their internal forces were balanced by the positive charge that was formed automatically around the orbit. The electrons possessed stable orbits, according to Gaussian Law. This positive charge is distributed equally across the atom.Īccording to Thomson, “negatively electrified corpuscles,” or electrons, are contained within the uniform mass of positive charge.Įlectrons could freely move within the atom. There is a source of positive charge that cancels out electrons’ negative charge. According to Thomas, the positive and negative charges were of equal magnitude, cancelling each other out and neutralising the atom. It is also possible to say that the electrons were randomly inserted in a positively charged sphere. We can also compare this to a watermelon, with the positive charge dispersed throughout the edible part of the watermelon and electrons studded in that sphere, as shown in the figure below: Thomson’s model diagram: He imagined electrons as dry fruits in a positive-charged sphere that represented the pudding.

The atom, according to Thomson’s model, is structurally similar to a plum pudding.

Thomson's atomic theory