Lec-03-Chap-02-1P

Lec-03-Chap-02-1P - Lecture 03 Atoms and Elements Atomic...

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1 Lecture 03 Atoms and Elements Atomic Structure and Subatomic Particles 2.1 The Nuclear Atom 2.2 Sizes of Atoms and Atomic Units 2.3 Uncertainty and Significant Figures 2.4 Atomic Numbers and Mass Numbers 2.5 Lecture 03, Knowledge and Skills • Know the basic types of radioactivity • Know the atomic subparticles • Know the nuclear model of the atom • Know and work with units • Understand the meaning of significant figures • Calculate with significant figures • Understand and work with atomic numbers and mass numbers Atomic Structure and Subatomic Particles • Atoms are composed of subatomic particles: • electron (e - ), proton (p + ) and neutron (n 0 ) • Key discoveries: Radioactivity Radioactivity • Becquerel (1896) • Uranium ore emits rays that “fog” a photographic plate • Marie and Pierre Curie (1898) • Marie Curie called the phenomenon radioactivity radioactivity Radiation Summary • Alpha Radiation • composed of 2 protons and 2 neutrons • creates element with atomic number 2 lower • Beta Radiation • composed of a high energy electron which was ejected from the nucleus • “neutron” converted to “proton” • creates element with atomic number 1 higher • Gamma Radiation • energy released from nucleus as the nucleus changes from higher to lower energy levels • no mass • no charge Electrons • Electric and magnetic fields deflect the beam • Gives mass/charge of e - = ± 5 .60 x 10 -9 g/C • Coulomb (C) = SI unit of charge • Joseph John Thomson (1897) discovered the e - : • “Cathode rays” • Travel from cathode (-) to anode (+) • Negative charge (e ± ) • Emitted by cathode metal atoms fluorescent screen – high voltage + cathode ray Electrons Millikan Oil Drop Experiment Charge on each droplet was: n ( ± 1 .60 x 10 -19 C) with n = 1, 2, 3,… n (e - charge) • Modern value = ± 1 .60217653 x 10 -19 C = ± 1 “atomic units” These experiments give: • Modern value = 9.1093826 x 10 -28 g = (-1.60 x 10 -19 C)(-5.60 x 10 -9 g/C) = 8.96 x 10 -28 g m e = charge x mass charge (Thomson)
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2 Protons • Atoms gain a positive charge when e - are lost • Implies a positive fundamental particle • At first, researchers did not know how the charges were organized
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Lec-03-Chap-02-1P - Lecture 03 Atoms and Elements Atomic...

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