The plum pudding model is an early 20th century model of an atom. It was later found to be wrong. It was proposed by J.J. Thomson in 1904, after the electron had been discovered, but before the atomic nucleus was discovered. During that time, scientists knew that there was a positive charge in the atom that balanced out the negative charges of the electrons, making the atom neutral, but they didn't know where the positive charge was coming from. Thomson's model showed an atom that had a positively charged medium, or space, with negatively charged electrons inside the medium. Soon after its proposal, the model was called a "plum pudding" model because the positive medium was like a pudding, with electrons, or plums, inside.