Explanation:
During the 19th century the accepted atomic model, was Dalton's atomic model, which postulated the atom was an "individible and indestructible mass".
However, at the end of 19th century J.J. Thomson began experimenting with cathode ray tubes and found out that atoms contain small subatomic particles with a negative charge (later called electrons). This meant the atom was not indivisible as Dalton proposed. So, Thomson developed a new atomic model.
Taking into consideration that at that time there was still no evidence of the atom nucleus, Thomson thought the electrons (with negative charge) were immersed in the atom of positive charge that counteracted the negative charge of the electrons. Just like the raisins embedded in a pudding or bread.
That is why this model was called the raisin pudding atomic model.
