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L35 - Atomic Emission Lecture 35 Electron Clouds Quantum...

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Lecture 35 Electron Clouds: Quantum model Key Idea: The distances of electrons from the nucleus are described in terms of probability. Atomic Emission Sr Ca Na Ba Astronomers use spectroscopy to identify the elements present in stars Emission and absorption spectra http://casswww.ucsd.edu/public/tutorial/Stars.html Ry = 2.18 x 10 -18 J/atom Visible: 0.15Ry - 0.22Ry Ultraviolet: 0.22Ry - 73Ry Ultraviolet absorption spectrum for hydrogen Absorbance 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 Light Energy (Ry) 0.75 Ry 0.89 Ry 0.94 Ry 0.96 Ry ionization 0.97 Ry Energy 0 n=1 n=2 n=3 n=4 -1.00Ry -0.06Ry -0.11Ry -0.25Ry Observable: light energy ! E = -Ry (1/n f 2 - 1/n i 2) Model of the H atom: E n = Ry (1/n 2 ) r = a o n 2 Energy and radius of the electron in H depend on “n” n = principal quantum # Ry = 2.18 x 10 -18 J/atom a o = 0.053 nm or 0.53 Å Why are the energies negative? How much energy is needed to remove the electron? -0.06Ry -0.11Ry -0.25Ry -1.00Ry -1.00Ry = 2.18 x 10 -18 J/atom = 1312 kJ/mol ultraviolet infrared visible Energy levels of hydrogen atom (not to scale)
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Bohr model of hydrogen atom and H emission spectrum n f =2 n i =5 n i =4 n i =3 486 nm 6.2 x 10 14 Hz 0.41 x 10
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