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Rutherford's Model Niels Bohr' Model of an Atom Rutherford’s Model Niels Bohr’ model of an atom Arvind Sir Luv Sir Suri Sir Theory Class: Tuesday Theory Class: Theory Class: Monday & Thursday (7pm) Wednesday & Saturday & Friday (7pm) MCQ Class: Saturday (7pm) MCQ Class: Tuesday (8pm) MCQ Class: Friday (8pm) (8pm) Daily Schedule Learning objectives: 1. Thomson’s model of an atom 2. Rutherford’s Model of an atom 3. Discovery of neutron 4. Niels Bohr’s model of an atom Quick Recap: ● Atoms are the fundamental particles of a matter. ● Electron was discovered by william crooke by cathode ray experiment. ● Thomson gave the idea of charge to mass ratio of electron by conducting the experiment on cathode ray tube. ● Anode rays or canal rays led to the discovery of proton by Goldstein Constituents Charge Mass Electrons -1.6022 × 10-19 C 9.1 × 10-31 kg Protons + 1.6022 × 10–19 C 1.67 × 10-27 kg Thomson Model: Postulates: 1. All atoms contain electrons. 2. The atom as a whole is neutral. The total positive charge and total negative charge must be equal. Drawback of this model. Can you answer this???? Rutherford’s 흰 particle scattering experiment: Rutherford conducted 흰-particles scattering experiments in 1909. Experimental setup: Can you answer why lead box was used along with alpha particle source? Observation: 1. Most of the alpha particles (99%) passes through it, without any deviation or deflection. 2. Some of the alpha particles were deflected through small angles. 3. Very few alpha particles were deflected by large angles and occasionally one out of 12000 alpha particles got deflected by 180o angle. Conclusion of Rutherford's scattering experiment: 1. Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected. 2. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space. 3. A very small fraction of α-particles were deflected by very large angles, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom. From the data he also calculated that the radius of the nucleus is about 105 times less than the radius of the atom. Rutherford's Nuclear Model Of Atom On the basis of his experiment, Rutherford put forward the model of an atom, which had the following features: 1. There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus. 2. The electrons revolve around the nucleus in well-defined orbits. 3. The size of the nucleus is very small as compared to the size of the atom. Rutherford's alpha particle scattering experiment shows the presence of nucleus in the atom. It also gives the following important information about the nucleus of an atom: 1. Nucleus of an atom is positively charged. 2. Nucleus of an atom is very dense and hard. 3. Nucleus of an atom is very small as compared to the size of the 4. atom as a whole. Drawbacks: 1. According to classical mechanics, any charged body in motion under the influence of attractive forces should radiate energy continuously. If this is so, the electron will follow a spiral path and finally fall into the nucleus and the structure would collapse. This behaviour is never observed. 2. It says nothing about the electronic structure of atoms i.e. how the electrons are distributed around the nucleus and what are the energies of these electrons. Discovery of neutron: In 1932 Chadwick proved its existence. He observed that, when a beam of alpha particles (He2+) is incident on Beryllium (Be), a new type of particle was ejected. It had mass almost equal to that of a proton ( 1.674 ×10–27kg) and carried no charge. Atomic number (Z) ● It is equal to the number of protons present in an atom ● It also represents the number of electrons in a neutral atom ● Eg. number of protons in Na atom = 11 So atomic number (Z) of Na = 11 Mass Number (A) The elementary particles (protons and neutrons) present in the nucleus of an atom are collectively known as nucleons. Mass number (A) = Number of protons(Z) + Number of neutrons(n) Note: The general notation that is used to represent atomic number mass number of an element is: A X Z Where, X – symbol of element A – Mass number Z – atomic number Isotopes, Isobars, and Isotones: Question: K-40, Ca-40, Ar-40 are the examples of: a. Isotopes b. Isobars c. Isotones d. Isomers Question: K-40, Ca-40, Ar-40 are the examples of: a. Isotopes b. Isobars c. Isotones d. Isomers Question: How did the actual results of the gold foil experiment differ from the expected results? a. There was no difference between the expected and actual results. b. Rutherford expected particles to travel through the atoms, but instead, they ricocheted and rebounded in unexpected directions. c. The alpha particles caused the gold foil to undergo nuclear fusion instead of fission. d. None of these answers are correct. Question: How did the actual results of the gold foil experiment differ from the expected results? a. There was no difference between the expected and actual results. b. Rutherford expected particles to travel through the atoms, but instead, they ricocheted and rebounded in unexpected directions. c. The alpha particles caused the gold foil to undergo nuclear fusion instead of fission. d. None of these answers are correct. Question: Name the part of an atom discovered by Rutherford α-particles scattering experiment 1. Electrons 2. Protons 3. Neutrons 4. Nucleus Question: Name the part of an atom discovered by Rutherford α-particles scattering experiment 1. Electrons 2. Protons 3. Neutrons 4. Nucleus Next Session: 1. EM waves 2. Plank's Quantum theory and exp Join Vedantu JEE Telegram channel NOW! Assignments Notes Daily Update https://vdnt.in/JEEVedantu .
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