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class23 - Today Matter waves Announcements No HW for next...

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Today: Matter waves! Announcements No HW for next week! Use the time for reviewing all we have done until now. (Exam 2 is on Tuesday 7:30pm) Exam preparation: Review Chapters 1-5, & Lasers (11.9, 11.10). There will be several questions on Chapters 1&2. Why is angular momentum quantized yet Newton’s laws still work? Why don’t electrons radiate when they are in fixed orbitals yet Coulomb’s law still Bohr model was a weird mix of classical physics and arbitrary rules… works? No way to know a priori which rules to keep and which to throw out… BUT IT WORKS (for certain things)! WHY is angular momentum quantized? WHY don’t electrons radiate when they are in fixed orbitals? How does electron know which level to jump to? Summary: What things CAN’T the Bohr model explain? (i.e. how to predict intensities of spectral lines) Can’t be generalized to more complex (multi- electron) atoms Shapes of molecular orbits and how bonds work Can’t explain doublet spectral lines Thomson – Plum Pudding Why? Known that negative charges can be removed from atom. Problem: just a random guess Rutherford – Solar System Why? Scattering showed a small, hard core. Problem: electrons should spiral into nucleus in ~10 -11 sec. Bohr – fixed energy levels Models of the Atom + Why? Explains spectral lines. Problem: No reason for fixed energy levels deBroglie – electron standing waves Why? Explains fixed energy levels Problem: still only works for Hydrogen. Schrodinger – quantum wave functions Why? Explains everything! Problem: None (except that it’s hard to understand) + + Thomson – Plum Pudding Why? Known that negative charges can be removed from atom.
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