Discovery of Subatomic Particles and Atomic Models
Discovery and Characteristics of the Electron
The properties of cathode rays are fundamentally independent of the environment in which they are produced. Specifically, these properties do not change regardless of the specific gas placed inside the discharge tube or the types of metals used to manufacture the electrodes. This consistency serves as clear evidence that the particles found in cathode rays are a universal component present in all substances. These particles are identified as electrons. J. J. Thomson was the scientist responsible for determining the ratio of electrical charge to the mass of an electron, commonly referred to as the ratio. His extensive work with discharge tube experiments was highly significant, leading to him receiving the Nobel Prize in Physics.
Discovery and Identification of the Proton
Eugen Goldstein conducted experiments using discharge tubes equipped with a perforated cathode, which led to the discovery of rays known as canal rays. These rays originated from the metal positioned at the positive side of the apparatus, the anode, and as a result, they were also designated as anode rays. Upon studying the characteristics of canal rays, Goldstein identified the presence of a positive charge within them. Unlike cathode rays, the behavior and properties of canal rays vary depending on the nature of the specific gases used within the discharge tubes. It was observed that the smallest and lightest positive particles among the canal rays were produced when the discharge tube was filled with hydrogen. Earnest Rutherford later discovered that this specific particle was a subatomic particle and provided it with the name proton.
J. J. Thomson’s Plum Pudding Model
The Plum Pudding Model was proposed by J. J. Thomson to describe the internal structure of the atom. According to this conceptual framework, an atom consists of a positively charged sphere in which negatively charged electrons are embedded, similar to the way ingredients are distributed in a pudding. A key feature of this model is the balance of electrical charges; the total number of positive charges within the sphere is equal to the total number of negative charges. Because these charges are equal and opposite, the atom as a whole is electrically neutral. Despite its initial importance, the Thomson model was eventually rejected as it failed to provide an adequate explanation for the results of subsequent scientific experiments.
Rutherford’s Gold Foil Experiment
Earnest Rutherford performed a groundbreaking experiment in which he bombarded a very thin gold foil with alpha rays, which carry a charge. To detect the behavior of these particles, a photographic film was arranged in a circular fashion around the gold foil. This setup allowed Rutherford to observe where the alpha particles struck after interacting with the foil. The experiment yielded three distinct observations that led to foundational assumptions about the structure of the atom.
The first observation was that the majority of the alpha particles passed directly through the gold foil. From this, the assumption was made that the most significant part of an atom consists of empty space. The second observation noted that some of the alpha particles experienced deflection as they crossed the foil. This led to the assumption that there is a positively charged region inside the atom that causes repulsion of the positively charged alpha particles. The third observation was that a very few alpha particles bounced back entirely, meaning they were deflected by a full . This critical finding led to the assumption that the entire positive charge of an atom is concentrated in a very small volume at the center of the atom, which Rutherford named the nucleus.