Chemistry 1B-01, Fall 2013 Lectures 1-2

Transcription

1 goals of lectures 1-2 Chemistry 1B Fall Nature of light and matter. Wave-particle duality chap.12 p lectures 1-2 (ch 12 pp ) 6th [ch 12 pp ] 7th The laws of nature in 1900 (successful for describing large objects) describe particles AND describe waves Experiments that contradicted these laws (when applied on the scale of atomic dimensions) Ultraviolet Catastrophe and Photoelectric Effect Spectrum of Hydrogen Atom Davisson-Germer and Compton Experiments particles BEHAVE AS waves waves BEHAVE AS particles obtain and use observed quantitative relationships (HW #1) Why? To understand the behavior of electrons in atoms an molecules 6 7 physics and chemistry in 1900 light waves fundamental particles and charge electron: - charge, m e = kg proton: + charge, m p = kg neutron: 0 charge, m n = kg [Table 2.2 and back cover] particles in general electromagnetic waves 8 9 properties of electromagnetic radiation (light WAVES) Planck s Formula electromagnetic wave fig 12.1 ~fig 12.2 (amplitude, wavlength, frequency) fig 12.3 (electromagnetic spectrum) spectrum of visible light HW#1 PROB 12.1 F2013 wave phenomena (properties of classical waves) dispersion [in a material light (EM waves) of differing frequencies will have differing velocities, different refractive indices ] refraction [bending of light (EM wave) when passing between materials of differing refractive index ] diffraction [EM waves bend when confined by a slit; diffraction pattern] interference [waves can interact constructively (add; reinforce) and destructively (subtract, cancel)] and Fig interference pattern] DON T FRET 10 Blackbody radiation- Fig 12.4 Ultraviolet catastrophe (p. 525) E=h ( per photon) (HW#1 PROB F2013, F2013 ) 11 1

2 some comments about ( sec 9.1, pp ) photoelectric effect (pp ) kinetic (HW #5.77 F2013 ; see p 168 KE AVG = (3/2)RT (per mole) KE AVG = (3/2)kT (per molecule) potential conservation of momentum (p. 158) units and conversions apparatus Sil Fig. 7.7 what s observed interpretation (HW# F2013 ) photoemissive material anode collector photoelectric effect : electron in a potential well (CLASSICAL: small amplitude, long wavelength) photoelectric effect : electron in a potential well (CLASSICAL: large amplitude, long wavelength) low amplitude wave (long l) attraction of metal large amplitude wave (long l) attraction of metal no electron ejected is work function (value depends on the metal being irradiated) example for potassium=3.68x10-19 J= 2.29eV 14 nada: no electron ejected (RED IS JUST A LOSER WAVELENGTH) CLASSICALLY: just increase amplitude to get enough to eject electron!! 15 photoelectric effect : electron in a potential well (= long) photoelectric effect : electron in a potential well ( = medium) low photon no extra for KE attraction of metal 3.59x10-19 J medium attraction of metal photon no electron ejected example: for potassium (depth of potential well ) = 3.59x10-19 J = 2.24eV example for potassium =3.59x10-19 J= 2.24eV photon of this : E=hn=hc/l l=(c/n)=(ch/e)=553 nm 16 (l=553nm color?) 17 2

3 photoelectric effect : electron in a potential well ( = short) summary of observations mucho extra for KE high attraction of metal photon KE of ejected electrons 0 = sec -1 l 0 = m = nm 0 = Cs cesium 0 = Na h h frequency of light ( ) sodium 0 = sec -1 l 0 = m = 504 nm 18 for given > 0 increase intensity of light more photons, but E per photon remains same more electrons, but of same kinetic 19 conservation of (p 527) if an individual photon does not have sufficient to kick electron out of the potential well of metal: NO ELECTRONS EJECTED!! if a individual photon that has sufficient to kick electron out of the potential well of metal: of photon= to get out of well + kinetic of electron spectrum of atomic hydrogen classical prediction (death spiral) observation of atomic spectra fig (HW# F2013, F2013 ) Bohr model (HW# a,d, 12.36, *12.39) fig , Silberberg Davisson-Germer experiment (shoot electrons at crystal (foil)??) wave-particle duality constructive int remember: WAVES showed constructive and destructive interference diffraction constructive by int slits and crystals diffraction of electrons- (Davisson-Germer Experiment; p. 530) De Broglie relationship (p. 528) (HW# ,12.33) x-rays electrons?? mind blowing What is meaning of electron wave?? ( ( Wavelengths of ordinary objects (p. 528, example 12.2) Silberberg Table 7.1 (HW# prob S2) Compton Experiment X-ray diffraction destructive of Al intfoil destructive int Electron diffraction of Al foil 22 Heisenberg uncertainty principle (p. 539) boing!! (HW# ) 23 3

4 goals of lectures 1-2 The laws of nature in 1900 (successful for describing large objects) describe particles AND describe waves Experiments that contradicted these laws (when applied on the scale of atomic dimensions) Davisson-Germer and Compton Experiments Ultraviolet Catastrophe and Photoelectric Effect Spectrum of Hydrogen Atom particles BEHAVE AS waves waves BEHAVE AS particles Ensuing quantitative relationships What to do?? invent quantum mechanics!!! Solvay Conference 1927 fuel for quantum mechanicians The mid-1920's saw the development of the quantum theory, which had a profound effect on chemistry. Many theories in science are first presented at international meetings. This photograph of well-known scientists was taken at the international Solvay Conference in Among those present are many whose names are still known today. Front row, left to right: I. Langmuir, M. Planck, M. Curie, H. A. Lorentz, A. Einstein, P. Langevin, C. E. Guye, C. T. R. Wilson, O. W. Richardson. Second row, left to right: P. Debye, M. Knudsen, W. L. Bragg, H. A. Kramers, P. A. M. Dirac, A. H. Compton, L. V. de Broglie, M. Born, N. Bohr. Standing, left to right: A. Piccard, E. Henriot, P. Ehrenfest, E. Herzen, T. De Donder, E. Schroedinger, E. Verschaffelt, W. Pauli, W. Heisenberg, R. H. Fowler, L. Brillouin quantum mechanics: WEIRD end of lectures

5 figure 12.1 Zumdahl figure ~12.2 wave amplitude wavelength (l) and frequency (n ) =c c=speed of light â 10 8 m s HW PROBS #12.22 F2013, Silberberg figure 7.2 Zumdahl figure HW PROBS #12.21 F2013, # wavelength and color Silberberg figure 7.5 and Zumdahl 12.7 constructive= high intensity destructive= low intensity R O Y G B I V ROY G BIV

6 Zumdahl figure 12.3 and Silberberg figure 7.6 Ultraviolet catastrophe Silberberg figure 7.7 classical decay and death of hydrogen atom Zumdahl figure 12.8 Silberberg figure 7.10 (emission: H-electron loses )

7 Silberberg figure 7.10 (absorption, H-electron gains ) Zumdahl figure Silberberg figure 7.5 and Zumdahl 12.7 from constructive= high intensity photons l= 402 nm electrons v= m sec -1 destructive= low intensity l increases x 1.5 v decreases x 1.5 l increases photons l= 594 nm electrons v= m sec -1 [slit 10-5 m] [slit m] Silberberg Table 7.1 wavelike properties of C 60 (fullerene) note mass in g, need to use kg for mvl=h (l correct in table)

8 waves: x vs v Uncertainty and measurement y x x V x V x x larger x smaller v x smaller v x larger particles in classical physics particles have mass (m), definite positions (x) and velocities (v) particles have kinetic and momentum p=mv particles obey Newton s laws of physics F=ma HW#1 PROB 12.1 F