In 1900 scientist concluded that the atom was not a simple, indivisible particle but contained sub-atomic particle – the electron represented as ‘e–’identified by J.J. Thomson. E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. These rays were positively charged radiations and made up of another sub-atomic particle. This sub-atomic particle had a charge, equal in magnitude but opposite in sign to that of the electron. Its mass was approximately 2000 times as that of the electron. It was given the name of proton represented as ‘p+’.
The mass of a proton is taken as one unit and its charge as plus one. The mass of an electron is considered to be negligible and its charge is minus one. The Structure of an Atom-- According to Dalton’s atomic theory the atom was indivisible and indestructible. But the discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of Dalton’s atomic theory. Then, It became necessary to know how electrons and protons are arranged within an atom. For explaining this, many scientists proposed various atomic models. J.J. Thomson was the first one to propose a model for the structure of an atom. Related ducuments 1. Download full document by: Delhi Public School, Mathura Refinery Nagar View /Download 2. [PPT] CHAPTER - 4 STRUCTURE OF ATOM - Galaxysite.weebly.com Download 3. Download E-Book based on Chapter: Chemistry in your future 4. Chapterwise Test paper solved or unsolved View then Download 5. Sample paper: View then Download
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