The history of atomic structure and quantum mechanics dates back to the times of Democritus, the man who first proposed that matter is composed of atoms. These theories could not gain much importance due to lack of technology. John Dalton’s atomic theory was a stepping stone that revived the idea of atoms.
For a long time it was believed that atoms are the ultimate particles that make matter and it cannot be divided further. The experiments during the latter part of nineteenth century and early years of the twentieth century revealed that even atom is not the ultimate particle. The continued efforts of the scientists led to the discovery of subatomic particles. The limitations of Dalton’s atomic model to explain certain observations formed the base for the discovery of electrons and protons. Further investigations revealed the existence of neutrons. The components of atoms are called subatomic particles. Let us now discuss the discovery of subatomic particles one by one.
Discovery of electrons
The discovery of electron is a result of continued sets of experiments and observations. Michael Faraday’s observations from a series of cathode ray discharge tube experiments in the mid-1850s revealed many facts. He observed that the cathode rays travelled towards anode from cathode. He used fluorescent materials to study the behaviour of these rays as they were invisible. His studies revealed that the cathode rays travelled in straight lines in the absence of magnetic and electric field. Based on the behaviour of these rays in magnetic and electric fields, Faraday concluded that the cathode rays consisted of negatively charged particles. He named these particles as electrons. J.J Thomson’s atomic model, also known as plum pudding model identified the existence of electrons as the subatomic particles. Thomson made precise calculations for the mass and charge on an electron and is credited for the discovery of electrons.
Discovery of neutrons and protons
Ernest Rutherford is credited with the discovery of protons. The experiments that led to the discovery of protons were based on electrical discharge in modified cathode ray tubes. The observations revealed that these particles (protons) were positively charged. The behaviour of protons in magnetic and electric field was exactly opposite to that observed for electrons. It was also found that the magnitude of charge on some of the positive particles was a multiple of fundamental unit of charge.
In the year 1932, James Chadwick discovered neutrons, another subatomic particle. He bombarded a thin sheet of beryllium by α-particles and found that electrically neutral particles with a mass slightly greater than that of the protons were being emitted. Chadwick called these particles as neutrons.
The advances in atomic structure and quantum mechanics have led to the discovery of other fundamental particles. The discovery of subatomic particles has been the base for many other discoveries and inventions. Go through the video given below to understand the atomic structure and learn more about Rutherford’s atomic model. Log on to Byju’s YouTube channel for more videos.