1/1000th of rays got strongly deflected because of a very strong positive charge in the centre of the atom he called this strong positive charge as “nucleus”.Few rays got reflected because of the repulsion of its positive with some other positive charge inside the atom.Since most rays passed through, Rutherford concluded that most of the space inside the atom is empty.One in 1000 rays got reflected by an angle of 180° (retraced path) after hitting the gold foil.A few rays got reflected after hitting the gold foil. Most of the rays just went through the gold foil making scintillations (bright spots) in the ZnS screen.ZnS screen is placed behind the gold foil.Alpha rays (doubly charged Helium He2+) were made to bombard the gold foil.A very thin gold foil of 1000 atoms thick is taken. Alpha ray scattering experiment Construction His atomic model is based on the Alpha ray scattering experiment. Thomson modified the atomic structure with the discovery of another subatomic particle called “Nucleus”. Also, further discoveries of other subatomic particles, couldn’t be placed inside his atomic model. Limitations of Thomson’s Atomic Structure: Thomson’s atomic model does not clearly explain the stability of an atom. the positive and the negative charges were of equal magnitude. Thomson’s atomic structure described atoms as electrically neutral, i.e. It is commonly referred to as the “plum pudding model” because it can be visualized as a plum pudding dish where the pudding describes to the positively charged atom and the plum pieces describe the electrons. Thomson described the atomic structure as a positively charged sphere into which negatively charged electrons were embedded. (e/m) for electron: 17588 × 10 11 e/bg.įrom this ratio, the charge of the electron was found by Mullikin through oil drop experiment. On applying the electric and magnetic field upon the cathode rays (electrons), Thomson found the charge to mass ratio (e/m) of electrons. With all this evidence, Thompson concluded that cathode rays are made of negatively charged particle called “electrons”.This proves that the cathode rays are made up of particles of a certain mass so that they have some energy. When rotor Blades are placed in the path of the cathode rays, they seem to rotate.When an external electric field is applied, the cathode rays get deflected towards the positive electrode, but in the absence of electric field, they travel in a straight line.This was confirmed by the ‘Fluorescent spots’ on the ZnS screen used. When a high voltage power supply is switched on, rays were emerging from the cathode towards the anode.cathode and Anode is fitted inside the glass tube. A high voltage power supply is connected using electrodes i.e. The role of the vacuum pump is to maintain “partial vacuum” inside the glass chamber. Cathode Ray Experiment – The discovery of electrons It has a tube made of glass which has two openings, one for the vacuum pump and the other for the inlet through which a gas is pumped in. The construction of working of the experiment is as follows: His work is based on an experiment called cathode ray experiment. He was later awarded the Nobel prize for the discovery of “electrons”. The English chemist Sir Joseph John Thomson put forth his model describing the atomic structure in the early 1900s. Thomson, Ernest Rutherford, and Niels Bohr. The most notable contributions to the field were by the scientists J.J. Each of these models had their own merits and demerits and were pivotal to the development of the modern atomic model. In the 18th and 19th centuries, many scientists attempted to explain the structure of the atom with the help of atomic models. In today’s class, we will be talking about atomic models.
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