An Evolution Of The Atomic Theory
Since radioactivity was discovered in 1898, the atomic theory of atoms has improved. These advancements are the foundation of much modern technology. These discoveries wouldn’t have been possible without the discovery of electrons, protons, and neutrons through four important scientists’ experiments.
In 1897, J. J. Thomson’s cathode-ray experiment led to the discovery of the e. Atomic theory began to emerge. Figure 1 shows a partially evacuated tube that Thomson used with an anode (c), and a cathode b at one end. The anode as well as the cathode were connected with a power source. An electric shock was applied to the cathode, and it produced negative cathode radiations (d). When a negative magnet (e), was placed beside the rays of electricity, it emitted negative cathode rays that traveled in a straight line (d). Protons are an important discovery in the theory of atomic physics. Rutherford, an American scientist, was puzzled about the structure of a nuclear atom in 1910. J.J. Thomson had suggested a model of the nuclear atom that was a “plumpudding model” (Figure 2), where the atom consists of a ball of positive charges with e– stuck in it. However, Rutherford wanted the experiment to prove his theory. The entrance was protected by a florescent screen and a radioactive source. Rutherford shot a- partials with thin gold foil, from the radioactive supply. He assumed they would all pass without any deflections. Figure 4. He saw some particles moving in a different direction than he expected, with some particles being bounced back. The observation showed that particles will drift off course if they are very close to the core, where all the positive energy is located. Rutherford identified the core as the nucleus. This is the part of the atom that makes up the majority of its mass and is composed of protons. Figure 5 shows the nucleus being surrounded with positive charges and having e-particles stuck to it.
Millikan returned to the electron job in 1911. Thomson had already determined the mass/charge for an e-, so he wanted to find the charge of each particle. Figure 6 shows Thomson’s oil droplet experiment. A chamber with a tiny hole at its bottom was filled with oil drops. An oil drop was placed into the small hole. After it passed through, it was examined by a microscope. The scientist monitored and manipulated the positive charges that passed through the holes to see how much of each charge was needed to balance the negative and positive charges. This allowed him to make the oil suspend mid-air. They could then determine the electron’s negative charge.
Rutherford was also puzzled by the fact that the atomic weight was higher than the total mass of protons, electrons and a substance. It could be due to a neutron particle. However, he never performed any experiments to prove it. Chadwick, who was challenged by the task, devised an experiment (Figure 7), in which he fired partials at a target made of beryllium. This released particles which fell onto paraffin and then released protons. His energy calculations showed that the particles emitted from beryllium due to the arrival on a- partials were uncharged. They are essentially the same weight as protons. He named them neutrons.
It would still be assumed that an atom is the smallest part of matter without these important developments in atomic theory. Technology would be stuck with John Dalton’s 1803 theory. It would also be impossible to have modern science or technology as current today without a brilliant experiment such as this.
