What did J.J. Thomson contribute to atomic theory?

J.J. Thomson is best known for his discovery of the electron, which was a significant milestone in atomic theory. His work in the late 19th century demonstrated that atoms are not indivisible spheres, as previously thought, but contain smaller negatively charged particles, which he called "corpuscles," later named electrons. This discovery provided evidence that the atom has internal structure and is made up of smaller components.

In addition to identifying the electron, Thomson proposed the "plum pudding model" of the atom. In this model, he suggested that negatively charged electrons are embedded within a positively charged "soup," which represented the rest of the atom. This model was an attempt to explain how these negatively charged particles could be held within the atom and helped to advance the understanding of atomic structure.

Thus, Thomson's contributions were pivotal in shifting the scientific view of the atom from a solid, indivisible entity to a more complex structure, leading to further development in atomic theory.