What was JJ Thomson's significant contribution to atomic theory?

J.J. Thomson's significant contribution to atomic theory was the discovery of electrons. Through his experiments with cathode rays in the late 19th century, Thomson demonstrated that these rays were streams of negatively charged particles, which he named electrons. This groundbreaking find suggested that atoms were not indivisible, as previously thought, but rather contained smaller, subatomic particles.

Thomson's work helped shift the understanding of atomic structure, showing that atoms are composed of charged particles and leading to the proposal of the "plum pudding model". In this model, electrons were thought to be embedded within a positively charged "soup," representing the atom's overall neutrality. This discovery was pivotal in advancing atomic theory by introducing the concept of subatomic particles and setting the stage for further developments in atomic models.