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Dalton's Atomic theory (in Hindi)
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Dalton's atomic theory

Vishwa Vivek Sharma
verified & star educator|| IIT-JEE NEET|| 5+ year experience|| hindi & English medium ||Chemistry || youtube- "Sharmaji education"

U
Unacademy user
Mam it was very good and quite enjoyable...please continue bringing up much more like these
Abhilasha Swarup
6 months ago
Thank you will surely do as you suggest.
Sir please share some important numericals with learners.
is this course completed sir ..???
Vishwa Vivek Sharma
10 months ago
Yes
Being COOL
10 months ago
thanku so much sir for ur reply !!!!!!!
  1. 55.5k views 4.9 2 2 unacadem Vishwa Vivek Sharma #21 Educator in IIT JEE chemical engineer || IIT-JEE NEET Mentorll 5+ year experiencell chemistry guru | youtube- "Sharmaji education 9.7k 753 Followers Following Courses


  2. Live classes IT JEE NEET Chemistry


  3. CHEMISTRY JEE MAIN/NEET NeutronNdkeusATOMIC Proton STRUCTURE Electron Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  4. CHEMISTRY JEE MAIN/NEET DALTON'S THEORY OF ATOM John Dalton developed his famous theory ofatom in 1803. The main postulates of his theory were Atom was considered as a hard, dense and smallest indivisible particle ofmatter. Each element consists ofa particular kind ofatoms. The properties ofelements differ because of differences in the kinds ofatoms contained in them. This theory provides a satisfactory basis for the law of chemical combination. Atom is indestructible, i.e., it cannot be destroyed or created. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  5. CHEMISTRY JEE MAIN/NEET Drawbacks It fails to explain why atoms of different kinds should differ in mass and valency etc. The discovery of isotopes and isobars showed that atoms of same elements may have different atomic masses (isotopes) and atoms of different kinds may have same atomic masses (isobars). The discovery of various sub-atomic particles like X-rays, electrons, protons etc. during late 19th century lead to the idea that the atom was no longer an indivisible and smallest particle ofthe matter. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  6. CHEMISTRY JEE MAIN/NEET DISCOVERY OF CATHODE RAYS & POSITIVE RAYS Cathode Rays Sir Willam Crooks studied various gases in a gas discharge tube (a glass tube with a very high potential applied to its ends) at low pressures. If the pressure in the tube is lowered to about 10 atm, glass begins to fluoresce (glow) faintly. It was established that the glow was due to bombardment of the glass by acertain kind ofrays emerging fromcathode (negative electrode) which travel in a straight line until they strike the anode (positive electrode). These rays Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  7. CHEMISTRY JEE MAIN/NEET Sir J. J. Thomson demonstrated that when cathode rays were deflected on to an electrometer, it acquired negative charge. He also showed that the rays were deflected on application ofan electric field. The cathode ray beam was deflected away fiom the negatively charged plate. These results were found to be identical, irrespective ofthe gas taken in the discharge tube. He concluded that the cathode rays were a stream of fast moving negatively charged particles called electrons (named by Stoney). He also calculated the velocity and specific charge for an electron. The specific charge is the ratio of charge to the mass of an electron, denoted as e/m ratio. The e/m ratio was found to be same for all gases. This led to the conclusion that the electron must be a fundamental or universal particle common to all kinds of the atoms. The e/m ratio (for an electron)1.758 x 101 C/Kg. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  8. CHEMISTRY JEE MAIN/NEET () J. Milikan determined the value of the charge on an electron with the help of famous Oil drop and the mass of an experiment. The magnitude ofthe charge on an electron = 1 .60206 x 10-19 C electron 9.1 x 10-31 kg. () You will be studying the details ofThomson's calculations ofe/mratio and Milikan's oil drop experiment for the determination of electronic charge later in Modern Physics in the Module of Physics Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  9. CHEMISTRY JEE MAIN/NEET Positive Rays Since the atom as a whole is neutral, it means that an equal amount of positive charged particle should also be there in the atom. Goldstein, by carefully expermenting with the discharge tube consisting ofperforated cathode, showed the presence of another type of rays. These rays emanating from anode passed through the perforations in the cathode. These carriedpositive charge and were called as positive or anode rays. It was established that these rays consist ofpositively charged particles called as protons. The magnitude ofcharge on a proton is same as that on an electron, but its mass was found to be 1837 times the mass of an electron. The mass ofa proton 1.6735 x 107 kg. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  10. CHEMISTRY JEE MAIN/NEET Since the electron has negligible mass (as compared to the proton), so it was assumed that whole mass of an atom is associated with the protons. Later in 1932, with the discovery ofneutron as IIIrd fundamental particle (Ist and IInd being electron and proton), it was established that the mass ofan atom is the total mass of protons and neutrons taken together. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  11. CHEMISTRY JEE MAIN/NEET Thomson's Model Putting together all the facts known at that time, Thomson assumed that an atom is a sphere of positive charges uniformly distributed, with the electrons scattered as points throughout the sphere. This was known as plum-pudding model at that time. However this idea was dropped due to the success of o-scattering experiments studied by Rutherford and Mardson Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  12. CHEMISTRY JEE MAIN/NEET Conclusions As most of the a-particles passed undeflected, it was concluded by Rutherford that the atom must be predominantly empty a-Particles are positively charged with appreciable mass 4 amu) and were moving high kinetic energy.In order to produce deflections, there must be some enomous positively charged body inside the atom. Only a few received large deflections. This led to the conclusion that enormous charge must be con fined to a very smallregion. This small region was given the name nucleus. Rutherford then proposed that an atom is composed ofa dense positive nucleus, thinly surounded by the electrons. The mass and the positive charge ofthe nucleus are confined in a very smallregion of space. The electrons are outside the nucleus, so that an atom is almost entirely empty space. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  13. CHEMISTRY JEE MAIN/NEET Failure of Rutherford's Model According to Classical Theory of Electromagnetism, whenever a charge is subjected to acceleration around an opposite charge, it emits radiation continuously. Hence the electron in Rutherford's atomwill loose energy and will not be able to stay in a circular path around the nucleus and should ultimately go into a spiral motion. Such an electron will fall into the nucleus. This, ofcourse, does not happen for electrons in an atom and the discrepancy could not be explained at that time. Later Niel Bohr, a student of Rutherford analysed atomic spectra of Hydrogen atom in terms ofQuantum Theory of Radiation and applied the results of Photoelectric Effect to it and developed a model ofatom which was widelyaccepted at that time. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  14. CHEMISTRY JEE MAIN/NEET Continuous Spectrum When sunlight (white light) is passed through a prism, it is dispersed or resolved into continuous spectra of colours. It extends from Red (7600 ) at one end to the Violet (3800 A) at other end. In this region, all the intermediate fiequencies between red and violet are present. This type ofspectrum is known as Continuous Spectrum. Hence continuous spectrum is one, which contains radiation of all the frequencies. A similar spectrum is produced when a rainbow forms in the sky. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  15. CHEMISTRY JEE MAIN/NEET The Quantum Theory of Radiation In 1901, Max Planck studied the distribution ofthe frequencies of radiations emitted fromthe hot bodies. He proposed a bold hypothesis that the radiant energy such as heat or light, is not emitted continuously but discontinuously in the form of small packets called as quanta. According to him, the energy of the electromagnetic radiation is directly proportional to the frequency of the radiation. The proportionality constant is called as Plancks constant (h). Ifenergy ofthe radiation is E, and the frequency of the radiation is v, then we have E-hv (The value of h is 6.626 x 10-34J-s) ris te mrt TE n (hv) Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  16. CHEMISTRY JEE MAIN/NEET Photoelectric Effect It was observed by Hertz and Lenard around 1880 that when a clean metallic surface is irradiated by monochromatic light ofproper fiequency, electrons are emitted from it. This phenomenon of ejectionofthe electrons from metal surface was called as Photoelectric Effect. It was observed that ifthe frequency of incident radiation is below a certain minimum value (threshold frequency), no emission takes place however high the intensity oflight may be. Another important feature observed was that the kinetic energy ofthe electrons emitted was indepen- dent of the intensity of the light. The kinetic energy of the electrons increase linearlywith the fiequency of incident light radiation. This was highly contraryto the laws ofPhysics at that time i.e. the energy of the electrons should have been proportional to the intensity of the light, not to the frequency These features could not be properly explained on the basis of Maxwell's concept of light i.e. light as electromagnetic wave. Follow me for Advance Chemistry Er. Vishwa Vivek Sharma


  17. CHEMISTRY JEE MAIN/NEET According to Einstein, when a quantum oflight (photon) strikes a metal surface, it imparts its energyto the electrons in the metal. In order for an electron to escape from the surface ofthe metal, it must overcome the attractive force of the positive ions in the metal. So a part ofthe photon's energy is absorbed bythe metal surface to release the electron, this is known as work fumction of the surface and is denoted by W The remaining part ofthe energy of the photon goes into the kinetic energy of the electron emitted. IfE, is the energy ofthe photon, KE is the kinetic energy ofthe electron and W, be the work function ofthe metal then we have Ei-KE + Wo (This is known as Einstein's photoelectric equation) Follow me for Advance Chemistry Er. Vishwa Vivek Sharma