Atomic Theory

J.J. Thomson's Atomic Model

With the discovery of the electron, the model of the atom had to be revised. Where would these electrons be found inside the atom? J.J. Thomson concluded that the atom would look something like plum pudding (as seen below), which is a British dessert served around Christmas.

As you can see, the "plums" (the old English term for raisins) are found stuck randomly in the pudding, similar to how the chocolate chips are placed randomly in a cookie. This is how Thomson believed the electrons to be found, stuck randomly in a positive jelly. The jelly had to be positive because the overall atom was known to be electrically neutral (i.e. no overall charge). Therefore, the plum pudding model of the atom is the atomic model that follows Dalton's model in history and is represented to the left.