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Slide 2 Slide 1 of 18 Chemistry 4.1 Section 4.1-2 Defining the Atom Part II Slide 3 Copyright Pearson Prentice Hall Slide 2 of 18 Defining the Atom 4.1-2 Cathode-ray tubes are found in TVs, computer monitors, and many other devices with electronic displays. Slide 4 Slide 3 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: Michael Faraday 4.1-2 1839: English Chemist Michael Faraday Suggested that the structure of atoms was somehow related to electricity. He proved that atoms contain particles that have electrical charges. Questions about electricity and charges on particles were answered in a few short years using a device called a Cathode Ray Tube or CRT. Slide 5 Slide 4 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: Eugen Goldstein 4.1-2 1886: German Physicist Eugen Goldstein In 1886, Eugen Goldstein observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles. Such positively charged subatomic particles are called protons. Slide 6 Slide 5 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: JJ Thomson 4.1-2 1897: English Physicist J. J. Thomson In 1897, the English physicist J.J. Thomson (18561940) discovered the electron using a cathode ray tube (CRT). Electrons are negatively charged subatomic particles. Slide 7 Slide 6 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 Thomson performed experiments that involved passing electric current through gases at low pressure. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode. Slide 8 Slide 7 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 Cathode Ray Tube Slide 9 Slide 8 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 A cathode ray is deflected by a magnet. Slide 10 Slide 9 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 A cathode ray is deflected by electrically charged plates. Slide 11 Slide 10 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 Using a CRT, Thomson discovered the following: A cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements. Both magnetic and electrical fields deflect the rays path in a CRT in a mathematically predictable way. Changing the gas or the material that the plates were made of effected his results. Slide 12 Slide 11 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 From this, Thomson proposed the following: Cathode rays are made up of - charged particles. Particles in a CRT came from the cathode plate. Atoms are not invisible balls, but had structure. Called these negative particles Electrons. Calculated the ratio of the electrons charge to its mass. Developed the atomic model called Plum Pudding. Slide 13 Slide 12 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: J. J. Thomson 4.1-2 Thomsons Plum Pudding Model: J. J. Thomsons model of the atom, he called Plum Pudding (thats what it reminded him of) had a sea of positive charge called the nucleus with electrons scattered throughout the atoms positively charged interior. However, this model did not last very long. Slide 14 Slide 13 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: Henri Becquerel 4.1-2 1896: French Physicist Henri Becquerel While working with Marie Curie and her husband, Pierre, accidentally discovered radiation. He accidentally placed a piece of potassium uranyl sulfate (radioactive material) on an unexposed film plate. He went to use the film plate, and when he developed the plate, all he saw was the outline of the material. Slide 15 Slide 14 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom II: Henri Becquerel 4.1-2 Because of his work, along with the work of Marie and Pierre Curie, all three received the Nobel Prize in Physics. Photographic Plate showing Radioactivity Slide 16 Slide 15 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom III: Robert Millikan 1909: American Physicist Robert Millikan Performed the famous Oil Drop experiment in order to measure the electrical charge on an electron. Unlike his colleagues before him, Robert Millikan was able to determine the charge of an electron using his famous Oil Drop experiment. 4.1-2 Slide 17 Slide 16 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom III: Robert Millikan Robert Millikans Oil Drop Experiment 4.1-2 Slide 18 Slide 17 of 18 Copyright Pearson Prentice Hall Defining the Atom > Models of the Atom III: Robert Millikan The oil drop experiment was an experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the electrical charge of an electron. The experiment entailed balancing the downward gravitational force with the upward bouyant and electric (charged) forces on tiny charged droplets of oil suspended between two metal electrically charged plates or electrodes. By repeating the experiment for many droplets, they were able to confirm that the charges were all multiples of some fundamental value, and calculated it to be the charge of a single electron. 4.1-2 Slide 19 Slide 18 of 18 Copyright Pearson Prentice Hall Defining the Atom > Thats All Folks ! !