There are various theories regarding the arrangement of sub atomic particles in an atom. Thomson’s model is one of them.
Thomson’s atomic model: This theory was proposed by J.J. Thomson in 1898. According to this model, positive charge of the atom spread over a sphere in which electrons are embedded to make atom electrically neutral.
He compares his model with the watermelon which is a nucleus and its seeds are the electron. This model is also known as plum pudding model. This model could not explain various phenomena regarding structure of atoms. So, this theory was discarded later on.