In this blog post, we will introduce the process of how the structure of atoms was discovered through the experiments and theories of scientists such as Thomson, Rutherford, and Bohr.
In the past, it was thought that matter was composed of small atoms that could not be broken down any further, but today we know that atoms are complex structures composed of electrons, protons, and neutrons. These discoveries were made possible by numerous experiments and research conducted as science advanced. Electrons, which carry a negative electric charge, are the smallest and lightest of the three particles. In 1897, Thomson discovered electrons by confirming the flow of negative electricity in a gas discharge tube experiment. Electrons with the same negative charge repel each other, making it difficult for them to gather inside atoms.
To explain why electrons do not scatter and maintain the form of atoms, Thomson proposed the “raisin bread model.” He thought that positive electricity was evenly distributed in atoms like bread dough, and electrons were scattered like raisins, so atoms were electrically neutral. This model was an important starting point for understanding the structure of atoms at the time, but further research was needed.
Protons, which carry a positive electric charge, are about 2,000 times heavier than electrons, making them difficult to separate or accelerate with small amounts of energy. However, new experiments became possible after Marie Curie discovered radium in natural minerals in 1898. Radium is a highly radioactive substance that emits positively charged alpha particles with high energy. In 1911, Rutherford conducted an experiment in which he collided alpha particles emitted from radium with thin gold foil. As a result, most of the alpha particles passed through the gold foil, but some were deflected and bounced off. Through this experiment, Rutherford realized that positive electricity was not spread throughout the atom like bread dough, but was concentrated in a very small area, which he called the “atomic nucleus.” Based on his experimental results, he proposed a “solar system model” in which positively charged atomic nuclei attract electrons and cause them to revolve around them, just as the sun attracts and causes the planets to revolve around it, thereby revising Thomson’s model.
However, Rutherford’s model could not explain the unique spectrum of each atom. In 1913, Niels Bohr proposed the “energy quantization hypothesis,” which stated that electrons can only orbit in specific orbits around the nucleus. This explained the spectrum of hydrogen atoms, which have a simple structure consisting of one proton and one electron.
Bohr’s hypothesis contributed greatly to the development of atomic models. In 1919, Rutherford confirmed the existence of protons in the nucleus through collision experiments on nitrogen atoms. He also predicted the existence of neutrons, electrically neutral particles in the nucleus. In 1932, Chadwick discovered neutrons, electrically neutral particles with a mass similar to that of protons.
This led to a deeper understanding of the structure of the atomic nucleus.
In 1935, Hideki Yukawa of Japan proposed the hypothesis that neutrons act as mesons to attract protons through nuclear forces. In atoms with multiple protons, protons with the same positive charge repel each other, and a force greater than this repulsive force is required to bind multiple protons to the nucleus. His proposal explained why protons do not scatter but remain bound together in the nucleus. This was a major advance in our understanding of the stability of the atomic nucleus.
As such, research on atomic structure has played a very important role in the history of science. From early simple models to modern complex models, scientists have constantly expanded our understanding through experimentation and research. These developments have had a major impact not only on physics but also on various other scientific fields such as chemistry and biology. Understanding atomic structure provides an important foundation for us to explore the nature of matter in greater depth and develop new technologies and applications.
