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Atomic Theory – Outline Notes First – How to write Outline Notes. http://www.quia.com/files/quia/users/mjalkut/outline-format http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CC0QFjAB&url=http%3A%2F%2Fahattaway.files.wordpress.com%2F2009%2F01%2Fch apter-11-basic-rules-of-outlinin1.doc&ei=dN4XU9mGNcnYqgGqvoAI&usg=AFQjCNE-RvRMahzPZaKDPuepRfCojLKVXQ&sig2=jILzZ855MoyfoXQJ_SVtQ&bvm=bv.62577051,d.aWM I. Atomic Theory is: scientific theory of structure & behavior of atoms. II. Atomic Theory: modified over time w/new discoveries about atoms. A. Around 450 BCE - Ancient Greek understandings of matter – 4 fundamental elements B. 1. Fire, air, water, earth 2. Characteristics of substances depended on ratios of these 4 things 3. This was NOT science – no experimentation. 460 BCE to 370 BCE - Democritus - ancient Greek who coined term “atomos” http://www.youtube.com/watch?v=NSAgLvKOPLQ (0:00 to about 3:00) 1. “Atomos”: source of word “atom” 2. “Atomos”: “uncuttable”, indivisible 3. Idea of “atomos” from thought experiments - what would happen if you kept cutting something pure in half forever? 4. This was NOT science – no experimentation. 5. Aristotle rejected this for the fire, air, water, earth elements so NOT accepted until 2000+ yrs later! C. 1803 Dalton – British teacher & scientist developed 1st modern atomic theory using recent experiments by others– SCIENCE! 1. Needed to explain ideas being discovered Go to Dalton’s Playhouse: http://www.visionlearning.com/en/library/Chemistry/1/EarlyIdeas-about-Matter/49/reading (use internet explorer) Discuss each new discovery and ask students to try to guess how the model changed because of that new information… 2. Joseph Priestly – Some substances are made of two or more different substances 3. Antoine Lavoisier’s - Law of Conservation of Mass Mass of reactants equals mass of products 4. Diamonds vs charcoal Things that look very different can be made of the same stuff 5. Dalton's theory had four main concepts: a) All matter is composed of indivisible particles called atoms. b) All atoms of a given element are identical; atoms of different elements have different properties. c) Chemical reactions involve the combination of atoms, not the destruction of atoms. d) When elements react to form compounds, they react in defined, whole-number ratios. D. 1897 JJ Thompson – Discovered the Electron (e-) http://www.youtube.com/watch?v=Rb6MguN0Uj4 1. Showed atoms were made of smaller parts a) 2. E. Cathode Ray Tube experiment (1) Ray bends when 2 metal plates connected to electricity (2) Ray bends toward the + plate so ray is made of neg stuff b) Tried again w/a magnet & ray bends in predicted way c) Tried with different metals and all gave off cathode rays Atom model changes a) e-s exist & are 1,000x smaller than H atom b) e-s are neg c) atoms usually neutral d) something must be + e) Plum Pudding (or blueberry muffin) model is result f) (Note: the density of the dough was thought to be light & fluffy) 1911 Ernest Rutherford – discovers nucleus http://www.youtube.com/watch?v=dNp-vP17asI 1. 2. 3. Gold Foil Experiment a) Shot tiny alpha particles at gold foil. b) Set up detector around foil to see where the alpha particles went c) MOST alpha particles went straight through… d) SOME particles veered to side or bounced backwards! These results helped to show: a) Atoms must be mostly empty space! b) There must be something sm & hard inside atoms! c) Atoms have a sm, dense nucleus d) Nucleus is probably + charged Later people also add the ideas that: a) Neg. electrons must be moving around quickly (so they don’t get pulled into the positive nucleus) b) F. Nucleus is made of sm particles called protons Discoveries about electrons http://www.youtube.com/watch?v=NSAgLvKOPLQ (5:45 to 8:15) 1. 1913 - Neils Bohr (Rutherford’s student)- Electrons in orbits Proposed e-s arranged in concentric circular orbits around nucleus like solar system (so also “planetary model”). 4 main ideas: a) e-s occupy only certain stable, stationary orbits around nucleus. b) Each orbit has an energy associated w/it. Orbit nearest nucleus has energy of E1, the next orbit E2, etc. c) Energy is absorbed when e-s jump from lower to higher orbits & energy is emitted when e-s fall from higher to lower orbits. d) The energy & frequency of light emitted or absorbed can be calculated by using the difference btwn the 2 orbital energies. 2. 1926 – Erwin Schrödinger – Quantum Mechanical Model Schrödinger used mathematical eqs to describe likelihood of finding an e- in a certain position. This model does not define the exact path of an e-. It predicts the odds of the location of the electron. Looks like a nucleus w/a e- cloud. G. a) e-s whiz around like hyper flies b) e-s sketched out particular shapes – orbitals c) Orbitals are not all spherical 1932 James Chadwick – discovers neutrons http://www.youtube.com/watch?v=_7DAlvRI1M4 1. There were problems with the last model: a) How do protons stay so close together? Shouldn’t they repel? b) Why is mass of 2 H atoms (w/1 P) < mass of 1 He atom (w/2 P)? Mass 4 H atoms = 1 He atom – why? c) Scientists could find no. of protons and mass of atoms, but they didn’t match! Why? 2. So Chadwick made an experiment where he shot metals with alpha particles. 3. a) Something shot out of metals! (particles!) b) Didn’t have a charge (not e- or p+) c) Made protons shoot out of wax! (so particles are fast & heavy) So, particles ~ same size & mass as protons, but w/no charge = neutrons! ----- break ----Quantum theory was a big focus during this time. (So was WWII.)It had more to do with understanding the levels of energy inside of atoms. This was a big deal because Einstein showed scientists that Newtonian physics was NOT complete. A lot more study was needed to understand what happens at the atomic level. We’re not going into this this year. You’ll get there later. Take physics! ----- break ----H. 1960’s - The Standard Model http://t3rfde.com/wp-content/uploads/2014/02/modern_atom_model.png 1. Many new tiny particles being discovered in particle accelerators 2. Murray Gell-Mann & George Zweig had idea of quarks. They said mesons & baryons made of 3 quarks or antiquarks, called up, down, or strange. 3. e-s shot at protons in a linear accelerator & the e-s seem to bounce off small hard cores inside the proton. James Bjorken and Richard Feynman analyze data which later is shown to provide evidence for quarks. 4. More evidence keeps coming from bigger particle accelerators, the latest was the discovery of the Higgs-Boson http://www.visionlearning.com/en/library/Chemistry/1 http://www.particleadventure.org/standard-model.html http://www.youtube.com/results?search_query=tyler%20dewitt%20chemistry%20atom&sm=3 http://www.particleadventure.org/other/history/earlyt.html