Chapter 2 - 2.1 Protons, Electrons and Neutrons Three...

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2.1 Protons, Electrons and Neutrons Three subatomic particles make up atoms: Protons (positive) and Neutrons (neutral). Found in the nucleus. Electrons (negative) Orbit the Nucleus. Account for most of atomic volume. *atoms have no net charge, that is the number of protons in an atom = the number of neutrons in an atom Electricity : There are two types of electric charge, positive and negative. They neutalize each other, which results in no charge. Like charges repel Unlike charges attract
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Radioactivity Henri Bacquerel : Noticed that uranium ores darken photographic plates, even while they are covered Marie and Pierre Currie : Isolate Polonium and Radium from Uranium ores. Notice that they emit the same type of rays that Bacquerel reported. This energy emission is radioactivity . Any element that emits this form of energy is said to be radioactive . There are three types of radiation : Alpha (α) particles: Positive ( 4 He nucleus) Beta (β) Particles: Negative (electron) Gamma (γ) radiation: pure energy, not a charged particle Proof : α and β particles deflect when they are passed through electrically charged plates ( + and – plates). γ rays remain straight. There is less deflection in alpha particles…this means that they have greater mass than beta particles. Proves that subatomic particles exist
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Cathode Ray Tubes: Air is removed There are 2 metal electrodes. One is a Cathode (this is a metal where there are excess electrons) The other is an anode (this is a metal where there is too few electrons, so it is positive) Excess electrons will jump off the cathode if hit with a strong enough voltage. These electrons will fly in a straight path to the positively charged anode. If charged plates are present, the path bends (toward + charge) This is a cathode ray. Cathode rays make gases glow, heat metal objects and cause fluorecent screens to flash. Cathode rays are electron beams
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Important Findings Using Cathode Ray tubes: JJ Thompson : Uses a cathode ray tube with charged plates and magnetic field coils to find the charge to mass ratio of 20 different metals (used at cathode). RA Millikan’s oil drop experiment : 1. A fine mist of oil drops is introduced into an upper chamber. 2. The oil droplets fall one by one into the lower chamber. 3. Gas molecules in the bottom chamber are split into + and – fragments by x- rays. 4. Electrons adhere to the falling oil droplets. 5. At the bottom of this chamber is a negatively charged plate. At the top of the chamber there is a positively charged plate. 6. By adjusting the voltage on the plates, the force of gravity on the droplet is
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This note was uploaded on 11/18/2010 for the course CHEMISTRY 4317 taught by Professor Cunycsichemistrydepartment during the Fall '08 term at Staten Island.

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Chapter 2 - 2.1 Protons, Electrons and Neutrons Three...

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