J.J. Thomson’s discovery of the electron in 1897 was a groundbreaking moment in the field of physics and fundamentally changed our understanding of atomic structure.
Thomson conducted a series of experiments using a cathode ray tube, which is a sealed glass tube from which most of the air has been evacuated. When a high voltage was applied across two electrodes, a stream of particles was emitted from the cathode, known as cathode rays. Thomson observed that these rays were deflected by electric and magnetic fields, indicating that they carried a negative charge.
To further investigate, Thomson measured the ratio of the charge to the mass of these particles. His experiments revealed that this ratio was much larger than that of hydrogen, the lightest known atom, which suggested that the particles were much smaller than any atom. From these observations, he concluded that cathode rays were composed of tiny, negatively charged particles, which he named ‘corpuscles’, later known as electrons.
Thomson’s work laid the groundwork for modern atomic theory and led to the realization that atoms are not indivisible, but rather consist of smaller subatomic particles. His discovery was a pivotal step in the development of quantum mechanics and has had lasting implications in the study of physics and chemistry.