What important ideas of atomic theory was J.J. Thomson credited with developing?
Thomson, who did much of his work at Cambridge University, is credited with demonstrating through experiment that atoms contained particles, and is credited with the discovery of the electron. Studying cathode rays in tubes containing gases, he argued that they were made of very tiny negatively charged particles, smaller even than atoms. He called these particles "corpuscles," though they would later become known as electrons. These "corpuscles" came from the gas in the tube. Because he understood that the overall atom was neutral in charge, he argued that it resembled a "plum pudding" in which the negative particles were suspended in a positive charge. His student Ernest Rutherford would later disprove this theory.