Rutherford's Atomic Model “Indigo blue is extracted from the indigo plant but is bluer than the plant it comes from” is a remarkable Chinese proverb that captures the essence of a student outshining the teacher A historic example happened in the field of chemistry, when Ernest Rutherford, hailed as the “Father of Nuclear Physics”, surpassed the prowess of his own mentor, J. J. Thomson, by providing a profound and superior understanding of atomic structure As we previously learned, atoms consist of three main components: protons, neutrons, and electrons These components were not all discovered at once, but rather through a series of hypotheses and experiments that led to revisions of the atomic models The early atomic model was proposed by J. J. Thomson in 1897, following the discovery of the electron and its mass Thomson hypothesized that the negatively charged electrons in an atom should be counterbalanced by positive charges to make the atom electrically neutral Therefore, he suggested a “Plum Pudding” atomic model He postulated that electrons are embedded in a lump of positively charged cloud, similar to raisins spread in plum pudding While this model succeeded in explaining the atom's neutrality, it hatched other questions, such as: how could two opposite charges coexist in an atom without being unstable? And since it is known that electron mass is so tiny, then what makes up the atomic mass? Ernest Rutherford, who was once a protege of Thomson at Cavendish Laboratory, sought to answer these questions through his gold foil experiment in 1909 Together with his coworkers, Hans Geiger and Ernest Marsden, he conducted an experiment in which a sample of radium was stored in a plumber box with a very small hole, emitting positively charged alpha particles through it The box was positioned in line with the thin gold foil that was surrounded by a zinc-sulfide screen While the alpha particles from the radium hit the gold foil, they scattered and produced light flashes that were detected by the screen Based on the plum pudding model, Rutherford thought that most of the particles would pass through the foil, while some are slightly deflected due to their encounter with electrons Initially, the experiment results were indeed consistent with his assumption But what followed next was totally unexpected! Some particles encountered large-angle deflections and very few (about 1 in every 20,000) were bounced backward! Rutherford thought there must be something positive, minuscule, yet heavy in the center of gold atoms that repels positive alpha particles and essentially makes up the atomic mass! He called it the atom’s nucleus This result strengthened the previous notion about the existence of positively charged particles later known as protons –within atoms And since the majority of the particles passed through, he suggested that an atom is mostly empty space Rutherford proposed an atomic model named "The Nuclear Model" based on this inquiry He stated that there is a tiny nucleus with positively charged particles inside and it is surrounded by electrons Different elements have different numbers of protons But in one atom, the proton amount is equal to the number of electrons revolving around the nucleus, making the atom neutral This model satisfyingly answered the questions that plum pudding model couldn’t explain, but it contradicts the principle of classical electrodynamics According to the principle, a charged particle in circular motion radiates energy continuously The electrons in this model move in circular motion and lose energy, causing them to spiral toward the center, and resulting in the collapse of the atom Yet in fact, none of these things happen Additionally, the energy-radiating particle must form a continuous atomic spectrum, but the observation showed a line spectrum Despite the limitations, Rutherford’s model provided a fundamental understanding of atomic structure, His intensive research about atoms and initial discovery awarded him the Nobel Prize We are still halfway through our journey on atomic model development In the upcoming video, as you guess, we’ll move forward a few years later to discuss the next model and how it helps refine Rutherford’s idea! Thank you for your continuous support! Especially our valued patrons and members who have been encouraging us to keep producing more quality contents!