Final answer:
J.J. Thomson's pivotal use of a cathode-ray tube in his experiments led to the discovery of the electron as a fundamental, negatively charged subatomic particle present in all atoms and to the determination of the electrons' charge to mass ratio.
Step-by-step explanation:
J.J. Thomson used a cathode-ray tube to learn that atoms had negative charges. In his experiments, Thomson passed an electric current through gases at low pressure within this tube. He observed that the cathode rays were attracted towards the positive electrode, indicating they were negative in charge. These rays were deflected by an electric field and also by a magnetic field when applied. As they moved from the cathode (negative electrode) to the anode (positive electrode), they demonstrated behavior expected of negatively charged particles, which Thomson eventually identified as electrons. Thomson's experiments were crucial in proving that electrons are fundamental, subatomic particles present in all atoms, leading to the demise of the notion that atoms are indivisible.
Adding further value to his work, Thomson determined the charge to mass ratio (qe/me) of an electron, which was a significant development in understanding the electron's properties. This ratio was derived by creating perpendicular electric and magnetic fields that acted on the electrons, allowing Thomson to calculate their velocity and overall charge-to-mass ratio by adjusting the strength of the electric field. His discovery marked a revolution in physics and chemistry, laying the groundwork for modern atomic theory.