Note for CHEM 201H at OSU 03
Popular in Course
Popular in Department
This 17 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at Ohio State University taught by a professor in Fall. Since its upload, it has received 17 views.
Reviews for Note for CHEM 201H at OSU 03
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/06/15
Chem 201H Prof Herbert Lecture 2 Particles Waves amp Quantization September 24 2010 Chapter 1 Sections 13 16 II PlanckEinstein formula II Particlewave duality l Atomic line spectra amp quantization II Uncertainty principle Notes 0 Problem set 1 will be posted later today 0 Sections 17 1 13 starting on Monday 0 Lab Expt 9 Emission Spectra Please come to lab With Title Objective and Procedure sections completed in your lab notebook but it is not necessary to do the prelab exercises Friday September 24 2010 The blackbody radiation problem What is the distribution of wavelengths as a function of temperature Classical physics predicts that it diverges as v gt 00 a result that is sometimes called the ultraviolet catastrophe L4 12 10 08 intensity 2er 06 04 02 00 5000 K classical theory 5000 K 4000 K 3000 K I l l 0 500 1000 1500 2000 2500 3000mm wavelength rim 139 lt V Friday Septemberzl 2010 Planck s solution 1900 Nobel prize in physics 1918 Max Planck had discovered an empirical formula that correctly predicts the intensity distribution at a given temperature In an attempt to derive this equation Planck assumes that the total energy of the black body is distributed into certain energy elements that are divided up among certain resonators oscillators according to their frequencies Thus he introduces E hv now known as the Planck Einstein relation where h is some previously unknown universal constant To fit the blackbody radiation spectrum he takes h 655 x 1034 J s The currently accepted value for Planck s constant is h 6626068 x 1034 J s Friday September 24 2010 Cosmic microwave background radiation Radialed Intensity per Unit Wavelength 168 Waitsm2per mm 12 I Data from the COsmic Background Explorer COBE 10 cynic nackgmund Exp a Planck s formula with T 27 K 87rhc 1 p T A3 ehcAkBT 1 08 06 04 02 00 05 1 2 5 Wavelength in mm 10 JC Mather eta AstrophysicaJourna354 L37 1990 Fllday Sepmtel 24 2mm The photoelectric effect Electrons are ejected from a metal surface that is exposed to electromagnetic radiation of sufficiently high frequency Radiant energy E fcuabted e am er Ultraviolet Metal radiation Electrons surface sour LC Posmve terminal Metal Current T indicator Voltage source Friday September 24 2010 5 The photoelectric effect Electrons are ejected from a metal surface that is exposed to electromagnetic radiation of suf ciently high frequency Ultraviolet radiation source Metal Electrons Additional Observations The minimum frequency of light that is necessary to generate current varies from metal to metal Current increases with the intensity brightness of the light Above the threshold frequency the kinetic energy of the ejected electrons increases as the frequency of the light increases may Elepmwtel 24 2mm Einstein s solution 1905 Nobel prize in physics 1915 The electromagnetic wave theory of light was well established by 1873 James Maxwell In contrast Einstein supposes that light comes in discrete packets now called photons with energies given by E hv Einstein further supposes that e ejection results from photon electron collisions that transfer momentum to the electrons If the energy transfer exceeds the e binding energy work function CD of the metal then the e is ejected with kinetic energy KE hv CD Friday September 24 2010 Photoelectric effect and the particlewave duality 556 10H Hz 539 nm KE gt 39 505 10 Hz 593 nm This suggests that electromagnetic radiation has certain characteristics of a particle eg momentum transfer to matter Other aspects of light are more consistent with a wave eg diffraction and interference This duality represents a failure of classical language which was developed to categorize macroscopic objects Friday September 24 2010 Atomic emission spectra line spectra CS quotIIIIIIIIII Hg III Ne 7 l w w mumI 500 700 400 600 nanometers Spectroscopy Energy in atomic and molecular systems is quantized ie these systems exhibit only a discrete set of energy levels E1 E2 E3 The field of spectroscopy is concerned with the absorption and emission of photons by matter Transitions between energy levels occur when an atom or molecule absorbs or emits a photon whose energy hv matches a difference between two energy levels A plot of these absorption or emission frequencies is called a spectrum I E2 E1 hV E2 I E1 E1 hv E2E1 hv quot M bu Absorption Emission Friday September 24 2010 10 Molecular spectroscopy Molecular spectroscopy refers collectively to techniques for measuring the frequencies v at which which molecules absorb or emit radiation Different types of energy level spacings rotational vibrational electronic correspond to different frequency or wavelength regimes and provide different kinds of structural information w l th 39 103 102 105 108 5x10 6 1040 1012 I l 3 0 if W 00 Buildings Humans HoneyBee Pinpoint Protozoans Molecules Atoms AtomicNuclei Frequency W H2 104 108 1012 1015 1016 1018 1020 Friday September 24 2010 11 Modern molecular spectroscopy Nowadays spectroscopy refers to various techniques for measuring the frequencies v at which which an atom or molecule absorbs or emits radiation Different types of energy level spacings correspond to different frequency or wavelength regimes and provide different kinds of structural information Small changes in a molecule s environment will slightly perturb its energy levels changing the frequencies at which it absorbs radiation Spectroscopy in various wavelength regimes provides an incredibly sensitive probe of molecularlevel structure hwy Friday September 24 2010 12 Hi i 1 emission Hydrogen line spectrum Balmer series Observed series of lines in Hatom emission A nm Balmer 1885 Paschen 1908 Lyman 1914 Brackett 1922 visible IR UV IR 656 1870 122 4050 486 1280 103 2630 434 1090 972 2170 410 1000 949 1940 954 937 1820 Fm ay Sepiem be 24 2010 Balmer n1 2 n2 345 1 1 Paschen m 3 n2 456 2 RH Lyman m 1 n2 234 Brackett m 4 n2 456 AE thH RH 1096776x107m1 n 713 Rydberg constant Observed series of lines in Hatom emission A nm Balmer 1885 Paschen 1908 Lyman 1914 Brackett 1922 visible IR UV IR 656 1870 122 4050 486 1280 103 2630 434 1090 972 2170 410 1000 949 1940 954 937 1820 Friday September 24 2010 Origin of the Rydberg formula Niels Bohr 1913 Suppose that H atom possesses certain discrete energy levels En n123 such that constant En 2 n n principal quantum number Note that E00 0 This corresponds to p and e at infinite separation ie ionization Note En lt O for finite n bound states of the atom 0 00 6 1 EhCRH r 4 5 Paschen 39 iiZCRH Energy gt hCRH 39 Principal quantum number n gt N Friday September 24 2010 15 b Bohr s model of the atom Nobel prize in physics 1922 n25 n24 n23 n22 n21 Wavelength Line spectrum Satellite models of atomic structure had been proposed previously but according to classical mechanics such arrangements are unstable Bohr proposed that only a discrete set of orbits were stable More precisely that angular momentum is quantized as L nh2rt The e can make transitions between allowed orbits by absorbing or emitting a photon of the appropriate frequency AE hv Although the term orbital is retained in homage to Bohr this is NOT a realistic picture of atomic structure Friday September 24 2010 16 Particlewave duality We have seen that light exhibits characteristics of both a particle and a wave This dichotomy is sometimes called the particlewave duality One implication of the Bohr model is that the stable orbits precisely accommodate an integer number of wavelengths 2nr n A This appears to imply wavelike properties for an electron The particlewave duality is an intrinsic feature of both matter and radiation Friday September 24 2mm 17
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'