This made him conclude that those negatively charged particles were atomic particles. He observed that this ratio was not dependent on the metal and the gas inside the tube. He made measurements of the length of the apparatus, the deflection, and the strengths of the magnetic and electric fields for the calculation of charge to mass ratio. On reaching the glass or touching the phosphorescent screen, it looks glowy as the Cathode rays absorb energy. The spread of this dark space occurs through the tube till it appears fuzzy. If the pressure is low (around 1 mm of mercury), the cathode rays look dark and slightly divergent near the cathode. He also noticed that if we adjusted the strengths of the magnetic and electric fields, no deflection was seen in the cathode rays. He observed that if the magnetic field is turned off, the electric field can deflect the beam. Nowadays, it is also called the ‘Electron Gun’.Įlectrons travel from the cathode that lies on the left-hand side of the tube to the phosphorescent screen on the right-hand side via the anode. The apparatus he designed was known as the Cathode Ray Tube. The aim was to conclude that cathode rays are negatively charged. Thomson to observe the nature of cathode rays. It also looks like a watermelon as the red edible part of the fruit can be compared to the positively charged sphere, while the black seeds dispersed in the fruit resemble the electrons in the sphere.Ī series of experiments was conducted by J.J. This is because, in this model, the electrons look like raisins embedded in a sphere of positive charge, just like a plum pudding looks. The atomic model proposed by Thomson looks like a watermelon or a spherical plum pudding. As the magnitude of the negatively charged particles and the positive amount is equal, they balance each other and, therefore, the atom is electrically neutral as a whole, carrying no charge. An atom is composed of negatively charged particles known as electrons.Īccording to these postulates of the Thomson Atomic Model, an atom looks like a sphere of positive charge containing negatively charged particles called electrons.They are neither positively nor negatively charged as the two types of charges inside them balance each other. Therefore, he proposed a model based on the properties of atoms that were known at that time. At that time, the nucleus of an atom had not been discovered. This is because it suggests that the electrons are dispersed in a positively charged sphere in the atom just like black seeds are dispersed in the red edible part of a watermelon. ![]() Of the many scientific models of an atom, the Thomson atomic model is the one we can compare with a watermelon in appearance. Thomson first demonstrated how air is ionised in X-rays. He also believed that an atom comprises a cloud of negatively charged particles in a sphere of positive charges. Thomson, electrons are 2,000 times lighter than a proton. The name “electrons” was given to these particles.Īccording to J.J. In 1897, he discovered negatively charged particles through the cathode ray tube experiment. ![]() Of the many scientists who proposed models for atomic structure, J.J. Later, the postulates proposed in the Dalton Atomic Theory were disapproved of because JJ Thomson discovered subatomic particles.īecause JJ Thomson discovered subatomic particles, the search for how these are arranged in an atom started. In this theory, he described atoms as indivisible particles, which means that they cannot be broken down into further smaller particles. Historyīefore the subatomic particles were discovered, Dalton’s atomic theory was given by John Dalton. ![]() This article is aimed at discussing this Thomson atomic model in detail. One of the early models of atoms, called the Thomson atomic model, has been compared to these food items in terms of appearance. You all must have seen a watermelon, a raisin pudding and a plum pudding in your daily lives.
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