Electron Discovery by J.J. Thomson

The question asks about the discovery of electrons. Understanding the history of atomic structure is key to answering this question correctly. The electron, a fundamental subatomic particle, was a groundbreaking discovery that changed our understanding of matter.

Thomson's Pivotal Electron Discovery

The discovery of the electron is widely credited to J.J. Thomson in 1897. Thomson conducted a series of experiments using cathode ray tubes. These experiments showed that cathode rays were streams of negatively charged particles, which he called "corpuscles." These corpuscles were much lighter than hydrogen atoms and were a fundamental part of all atoms.

• Cathode Ray Tube Experiment: Thomson observed that cathode rays were deflected by both electric and magnetic fields.
• Charge-to-Mass Ratio: By measuring the deflection, Thomson was able to determine the charge-to-mass ratio (\(\frac{e}{m}\)) of these particles. He found this ratio to be constant, regardless of the gas used in the tube or the metal used for the electrodes. This suggested that these particles were universal constituents of matter.
• Universal Particle: His findings indicated that these negatively charged particles, later named electrons, were present in all types of atoms, proving that atoms were not indivisible as previously thought.

Contributions of Other Scientists

It is important to understand the contributions of the other scientists listed in the options to differentiate their work from Thomson's electron discovery:

• E. Goldstein: Goldstein worked with cathode ray tubes before Thomson. In 1886, he observed "canal rays" or "anode rays," which were streams of positively charged particles. His work was crucial in the later discovery of the proton, but he did not discover the electron.
• J. Chadwick: James Chadwick discovered the neutron in 1932. The neutron is another fundamental subatomic particle, found in the nucleus of atoms, which has no electric charge.
• Neils Bohr: Neils Bohr proposed a quantum model of the atom in 1913, often referred to as the Bohr model. This model explained the stability of atoms and the emission spectra of hydrogen, but he did not discover the electron itself. His work built upon the understanding of electrons already established by Thomson and Rutherford.

Summary of Electron Discovery

In summary, J.J. Thomson's experiments with cathode rays definitively proved the existence of the electron as a fundamental, negatively charged subatomic particle. His work was a crucial step in developing modern atomic theory and understanding the structure of the atom.