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What are atoms? Describe them.

What are atoms? Describe them. Models of the Atom.

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What are atoms? Describe them.

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  1. What are atoms?Describe them.

  2. Models of the Atom

  3. JJ THOMSON MODEL 1907 PLUM PUDDING J.J.Thomson that atoms contained p+ and e-.But neutral atoms must contain equal numbers of p+ & e-.Thomson proposed that inside an atom was a mixture of equal numbers of p+ and e-, scattered randomly, just as raisins and currants are found inside a plum pudding.

  4. Plum Pudding Model

  5. Rutherford Model Lord Ernest Rutherford learned from experiments that atoms contained a very small but heavy central positive nucleus. In 1911 he proposed the model that inside an atom all the protons were gathered at the center (nucleus) of the atom, with the electrons scattered randomly around.

  6. Most a particles went straight through, but the ones that passed closest the Au nucleus were progressively more deflected.

  7. The fact that most alpha particles pass straight through the foil suggests: • The nucleus is positive • The nucleus is negative • The atom is mostly empty • The particles have lots of energy.

  8. The fact that some alpha particles were deflected by the foils suggests: • The nucleus is positive • The nucleus is negative • The atom is mostly empty • The particles have lots of energy.

  9. Gold foil experiment : atom is mostly empty space with dense positively charged nucleus. Electrons move in circular orbits about the nucleus.

  10. Rutherford felt the inertia from circular velocity of e- would balance the electrostatic attraction of the nucleus.

  11. Flaws: Maxwell had proved that accelerated charges radiate EM energy. Circular motion is acceleration.The e- should lose energy & spiral into the nucleus.That does not happen!Also, how did the positive nucleus stay together?

  12. Bohr Model There are several allowed orbits that an e- can occupy. The orbits are at varying distances from the nucleus. Closest orbit n=1, the ground state. E=0 for e-

  13. Orbits further from the nucleus require the e- to absorb E to occupy. If e- in higher orbit, atom said to be excited.

  14. Atoms need to absorb E to excite e- to higher orbits. When e- drops to lower orbit atom gives off E.

  15. Evidence for Bohr Mode from Spectra • Absorption- e- absorbs specific photon E. • Emission - e- emits specific photon E.

  16. Electric E supplied to gas tubes causes gases to emit light.

  17. Emission SpectrumWhen viewed through a prism or spectroscope, we see only certain l of light are emitted by each element. Bright Line Spectra

  18. Absorption Continuous spectrumFrom sunlight

  19. Absorption SpectrumWhen light is passed through cool gasses, each gas absorbs only certain l’s of light. When viewed through a prism, the same l’s that are emitted by each element, are absorbed by each element.

  20. Frequencies emitted exactly match the frequencies absorbed.

  21. Do Now: A photon with an unknown energy hits a metal with Wo 2.11 x 10-19 J. The max KE of the photoelectrons 2.0 x 10-19 J. What is the color on the incident photon? • Epho = Wo + KE. • Epho = 2.11 x 10-19 J + 2.0 x 10-19 J. • Epho = 4.11 x 10-19 J • E = hf. • f = 6.2 x 1014 Hz.

  22. Review • How does Rutherford view the atom? • How does Bohr view the atom?

  23. Rutherford Assumptions • Atom has dense + nucleus • Tiny, low mass negative e- orbit in shells. • Atom mostly empty space. • Evidence: most +alpha particles passing straight through gold foil. • Some deflected or repelled straight back.

  24. Bohr Assumptions: • Each atomic orbit is associated with a specific E level for e-. It is quantized. • Innermost orbit is “ground state” • When atom absorbs photon energy e- “jump” to higher E outer orbits. Atom is “excited”. • Atom emits photons when e- “fall” to lower inner E orbits. • No in between orbits possible, photons absorbed/emitted comes in discrete E amounts.

  25. Bohr ModelEmission & absorption spectra form from e- either emitting or absorbing EM energy photons as they change orbits.

  26. How stuff works. How is light produced? 2:15 • http://www.youtube.com/watch?v=GCvjo3em7EQ

  27. The frequencies/colors of the observed spectral lines correspond to the exact energies (E=hf) that e- are absorbing or emitting as they move between allowed orbits in the atom.

  28. Film: Quantum Mechanics & Atomic Structure 6:20 minutes http://www.youtube.com/watch?v=-YYBCNQnYNM Hwk Concepts: Rd Tx 840 – 847 Do pg 847 #2 – 6 Full Sentences & Mult Choice sheet.

  29. Bohr Energy Diagrams

  30. Orbital Energy Levels/ Ionization Energy Each orbit is associated with a specific energy which corresponds to the minimum energy needed to totally strip an e- from that orbit. This ionizationenergy > E needed to jump between orbits. If an atom absorbs E = to the orbit energy it becomes ionized (charged). Orbits are named by quantum number.

  31. Ionization Energy: e- stripped from atom if photon with sufficient energy absorbed.

  32. When e- is in lower/closer orbits to nucleus. It takes more E to ionize/strip it out of atom.

  33. Ex 1: How much energy would be needed to ionize (completely strip) an electron:In the n=1 level of of Hydrogen?in the n = b or level of Mercury?In the n = 2 level of Hydrogen?

  34. For e- to jump to higher orbits it must absorb exactDE between orbits.

  35. The photon energy absorbed & emitted during transitions between e- orbits:

  36. Use diagrams to find DE.Ephoton = Ei - EfUse Epho = hf of the radiationto find frequency associated with photon of known energy.

  37. Ex 2:a) How much E is absorbed when a Hydrogen e- jumps directly from the n=1 to n=3 orbit?b) How much E is released when the Hydrogen e- drops from n=3 to n=1?c) When the e- drops back down to the n=1 from n=3 orbit, what f photon is emitted?d) To which type of radiation does that photon correspond?e) How many different photons are possible to be emitted by electron dropping from the n=3 to n=1 level?

  38. n =3 to n = 1 Ephoton = Einitial - Efinal. -13.6 eV - (-1.51 eV)= -12.1 eV (12.1 eV)(1.6 x 10-19 J/eV) = 1.936 x 10-18J.E = hf. f = E/hf = 1.936 x 10-18J/(6.63 x 10-34 Js)f = 2.92 x 1015 Hz. Look up.

  39. Ex 3: A Mercury Atom has an e- excited from the n=a to the n=e energy level. • What is the frequency it will absorb? • To which radiation does the frequency correspond? • If the e- drops down from the e to the b level, what type of radiation will it emit. 1.61 x 10 15 Hz UV Orange

  40. Read Rev Book pg 333 – 334do pg 334 “try it 1-3” & 338 #17 -19, 22-23, 26-27, & 30, 32 – 34Write out equations, calculations with units on separate sheet for credit. Hwk check.

  41. Film: Quantum Mechanics & Atomic Structure 6:20 http://www.youtube.com/watch?v=-YYBCNQnYNM&annotation_id=annotation_990931&feature=iv

  42. Equivalence of Mass & Energy

  43. Einstein: “EM E, acts like tiny bit of matter, at the smallest scale matter/energy same thing”.E stored in the nucleus of mass obeys Einstein’s equation: E = in J. E = mc2. m = mass kg c = 3 x 108 m/sE can be released when nucleus is transformed.

  44. Ex 1: How much energy is produced when 2.5 kg of matter are completely converted to energy?How much energy is that in eV?

  45. E = mc2.=(2.5 kg )(3x108 m/s)2. = 2.25 x 1017 Jin eV(2.25 x 1017 J)(1 eV / 1.6 x 10 –19 J) = 1.4 x 1036 eV.

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