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Chemistry 4.2 Slide 1 of 25 4.2 Structure of the Nuclear Atom > Subatomic Particles Three kinds of subatomic particles are electrons, protons, and neutrons. Slide 2 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles Electrons In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron. Electrons are negatively charged subatomic particles. Slide 3 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles 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 4 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles Cathode Ray Tube Slide 5 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles A cathode ray is deflected by a magnet. Slide 6 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles A cathode ray is deflected by electrically charged plates. Slide 7 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Let’s go to the videotape Slide 8 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Thomson’s Conclusions Thomson found: 1.The charge to mass ratio of the particle 2.Various metals produced the exact same cathode ray (same charge to mass) 3.Various gases produced the exact same cathode ray (same charge to mass) Slide 9 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles Thomson concluded that a cathode ray is a fundamental particle contained in all matter. It is made of a stream of electrons. Electrons are parts of the atoms of all elements. Slide 10 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Robert Millikan Slide 11 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Let’s go to the videotape!! Slide 12 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Robert Millikan Millikan determined: 1.The charge on an electron. 2.The fundamental charge of matter. 3.He calculated the mass of an electron from Thomson’s charge to mass ratio. Slide 13 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Conclusions •Atom is divisible •One of the basic subatomic particles is the negatively charged electron •Atom is electrically neutral, so it must contain positive charges to balance out the electrons •Electrons have an extremely small mass, therefore there must be other massive particles in the atom Slide 14 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles Protons and Neutrons In 1886, Eugen Goldstein (1850–1930) 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 15 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus J.J. Thompson and others supposed the atom was filled with positively charged material and the electrons were evenly distributed throughout. This was called the “plum pudding model,” but you can think of it as the “chocolate chip cookie model.” This model of the atom turned out to be shortlived, however, due to the work of Ernest Rutherford (1871–1937). Slide 16 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus Rutherford’s Gold-Foil Experiment In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil. Slide 17 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus Rutherford’s Gold-Foil Experiment Slide 18 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus Alpha particles scatter from the gold foil. Slide 19 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Video Slide 20 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus The Rutherford Atomic Model Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus. The nucleus is the tiny central core of an atom and is composed of protons and neutrons. Slide 21 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > The Atomic Nucleus Rutherford suggested that the nucleus contained a particle with a positive charge the proton. Atoms of different elements have different numbers of protons giving their nuclei different charges. That meant the hydrogen nucleus (it has one proton) was an elementary particle. Rutherford named it the proton, from the Greek word "protos," meaning "first." Slide 22 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles In 1932, the English physicist James Chadwick who had worked with Rutherford (1891–1974) confirmed the existence of yet another subatomic particle: the neutron. Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton. Slide 23 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Chadwick fired the neutrons at a block of paraffin wax, which has a high concentration of hydrogen and is therefore rich in protons. Some of the neutrons collided with protons in the wax and knocked them out. Chadwick could then detect these protons and measure their energy. Using his knowledge of energy and momentum, he was able to work out the mass of the neutrons from the range of energies of the protons that they knocked out. Slide 24 of 25 © Copyright Pearson Prentice Hall Structure of the Nuclear Atom > He found that its mass was slightly more than that of a proton. Chadwick, like Rutherford, used an ingenious method to probe into what cannot be seen. To the Videotape!!!!! Slide 25 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > The Atomic Nucleus In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom. Slide 26 of 25 © Copyright Pearson Prentice Hall 4.2 Structure of the Nuclear Atom > Subatomic Particles Table 4.1 summarizes the properties of electrons, protons, and neutrons. Slide 27 of 25 © Copyright Pearson Prentice Hall 4.2 Section Quiz Assess students’ understanding of the concepts in Section 4.2. Continue to: -or- Launch: Section Quiz Slide 28 of 25 © Copyright Pearson Prentice Hall 4.2 Section Quiz 1. Which of the following is NOT an example of a subatomic particle? a. proton b. molecule c. electron d. neutron Slide 29 of 25 © Copyright Pearson Prentice Hall 4.2 Section Quiz 2. The nucleus of an atom consists of a. electrons only. b. protons only. c. protons and neutrons. d. electrons and neutrons. Slide 30 of 25 © Copyright Pearson Prentice Hall 4.2 Section Quiz 3. Most of the volume of the atom is occupied by the a. electrons. b. neutrons. c. protons and neutrons. d. protons. Slide 31 of 25 © Copyright Pearson Prentice Hall END OF SHOW