102 lect24_handout

102 lect24_handout - Physics 102: Lecture 24 Bohr vs....

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Physics 102: Lecture 24, Slide 1 Bohr vs. Correct Model of Atom Physics 102: Lecture 24
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Physics 102: Lecture 24, Slide 2 Early Model for Atom But how can you look inside an atom 10 -10 m across? Light (visible) λ = 10 -7 m Electron (1 eV) λ = 10 -9 m Helium atom λ = 10 -11 m - - - - + + + + • Plum Pudding – positive and negative charges uniformly distributed throughout the atom like plums in pudding
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Physics 102: Lecture 24, Slide 3 Rutherford Scattering Scattering He ++ atoms off of gold. Mostly go through, some scattered back! Atom is mostly empty space with a small (r = 10 -15 m) positively charged nucleus surrounded by cloud of electrons (r = 10 -10 m) (Alpha particles = He ++ ) Plum pudding theory: + and – charges uniformly distributed Æ electric field felt by alpha never gets too large To scatter at large angles, need positive charge concentrated in small region (the nucleus) +
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Physics 102: Lecture 24, Slide 4 Nuclear Atom (Rutherford) Classic nuclear atom is not stable! Electrons will radiate and spiral into nucleus Need quantum theory Large angle scatterings nuclear atom
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Physics 102: Lecture 24, Slide 5 Recap • Photons carry momentum p=h/ λ • Everything has wavelength λ =h/p • Uncertainty Principle Δ p Δ x > h/(2 π) •A t o m – Positive nucleus 10 -15 m – Electrons “orbit” 10 -10 m – Classical E+M doesn’t give stable orbit – Need Quantum Mechanics! Bohr model (1913)
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Physics 102: Lecture 24, Slide 6 Bohr Model is Science fiction The Bohr model is complete nonsense. Electrons do not circle the nucleus in little planet- like orbits.
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102 lect24_handout - Physics 102: Lecture 24 Bohr vs....

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