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BELL WORK • What were the two most popular experiments that helped develop the atomic model and theory? • What is an isotope? • What makes isotopes different? STRUCTURE OF THE ATOM MR. SCHLAMB THE NUCLEUS • https://www.youtube.com/watch?v=FSyAehMdpyI CATHODE RAY TUBES • These cathode ray tubes led to the first discovery of a subatomic particle the electron • It was found that when the ray was exposed to a negative electric field the ray would bend away from the field • This led to the conclusion that negatively charged particles composed the ray and these became named electrons INFERENCES BASED ON ELECTRONS 1. Since atoms are electrically neutral they must contain a positive charge to balance the negative electrons 2. Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass • With this knowledge the first model of the atoms was purposed PLUM PUDDING MODEL RUTHERFORD GOLD FOIL EXPERIMENT • This led to the discovery of the atomic nucleus • https://www.youtube.com/watch?v=_uEFKG122dA • Rutherford concluded that the center of an atom which he called a nucleus contained positive particles but was confused on where the electrons were NIELS BOHR • One of Rutherford's associates purposed a new model for the atom: Bohr’s model OIL DROP EXPERIMENT • https://www.youtube.com/watch?v=UFiPWv03f6g NUCLEUS • Usually like charges repel but in the nucleus 83 protons can exist and the nucleus still be stable • The force that holds an atomic nucleus together is referred to as nuclear forces ISOTOPES • Isotopes have the same number of protons but a different number of neutrons • This difference in neutrons changes the mass number