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UGA CHEM 1211 - Chapter 6

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Slide 1Slide 2Slide 3Electromagnetic RadiationSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Einstein and the Photoelectric EffectPhotoelectric EffectPhotoelectric EffectPhotoelectric Effect6.3 Atomic Line Spectra and Niels BohrSlide 16Slide 17Slide 18Balmer equationSlide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26The Bohr Model of the AtomSlide 28Energy LevelsEnergy LevelsEnergy LevelsSlide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 531s, 2s-OrbitalsSlide 55p-orbital (p stands for principal)Slide 57Slide 58d-orbitals (d is diffuse)Slide 603dxy, 3dxz, 3dyz-Orbital3dx2- y2 & 3dz2-Orbitalf-orbital (f is fundamental)Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Ch. 6 The Structure of Atoms6.1 Electromagnetic RadiationElectromagnetic Radiation or “Light” is composed of two orthogonal vectors: An electric wave and a magnetic wave.1Vibrating electric and magnetic fields at right angles to each other.•The wavelength of EM radiation has the symbol .•Wavelength is the distance from the top (crest) of one wave to the top of the next wave. –Measured in units of distance such as m, cm, nm, Å, etc.–1 Å = 1 x 10-10 m = 1 x 10-8 cm23•The frequency of electromagnetic radiation has the symbol .•Frequency is the number of crests or troughs that pass a given point per second (like water waves hitting the pier).–Measured in units of 1/time – 1/s - s-1 - Hertzl = speed of propagation of the wave or = c (for light)c = speed of light (3.00 x 108m/s) [in a vacuum, speed of light for all λ is the same]Wavelength and frequency are inversely proportional to each other, for the same wave, shorter wavelengths correspond to higher frequency.4Electromagnetic Radiation•The relationship between wavelength and frequency for any wave is velocity = .•For electromagnetic radiation the velocity is 3.00 x 108 m/s and has the symbol c.•Thus c =  for electromagnetic radiation.UV: shorter λ, higher νIR: longer λ, low νHigh Energy; High Frequency; Short λ or Low Energy; Low Frequency; Long λClicker Q: Which has the highest frequency?A. γ-rays B. x-rays C. IR D. long radio wavesClicker Q: Which has the lowest energy?56Clicker Q: What is the frequency of green light of wavelength 5200 Å?  = c (for light)c = 3.00 x 108 m/s 1 Å = 1.00 x 10-10 mPress log button then enter that number. No e notation.6.2 Quantization: Planck, Einstein, Energy, and PhotonsPlanck’s equationE: energy, in Joules/photonh: Planck’s constant, 6.626 x 10-34 J s∙ν: frequency (units of Hertz, 1/s or s-1)E = hν = hc/λLight with long λ (low ν) has low energy (E).Light with short λ (high ν) has high energy (E).As the frequency of light increases, the energy of the photon increasesAs the wavelength of light increases, the energy of the photon decreases7UV light has a ν = 2.73 x 1016 1/s, what is its energy?Clicker Q: Yellow light has a ν = 5.27 x 1014 1/sEnergy? Enter as #.##e#A laser having a wavelength of 508 nm emits 4.28 x 1017 photons of light per second. How much energy, in Joules, does this laser emit in 5.00 seconds?The energy of a particular color of red light is 2.92E-22 kJ. What is the wavelength of this light in nanometers.10•Certain metals will release (eject) electrons when light strikes the metal surface.•The energy of the light must exceed a minimum or “threshold energy” for this to occur.•Any excess energy beyond this minimum goes into the kinetic energy of the ejected electron. (They fly away with greater velocity)A. Einstein (1879-1955)Einstein and the Photoelectric Effect•Classical theory suggests that energy of an ejected electron should increase with an increase in light intensity.•This however is not experimentally observed!•No ejected electrons were observed until light of a certain minimum energy is applied.•Number of electrons ejected depends on light intensity so long as the light is above a minimum energy. (This “minimum energy” is also the ionization energy of the metal.)Photoelectric EffectExperiment demonstrates the particle like nature of light.Photoelectric Effect•Conclusion: There is a one-to-one correspondence between ejected electrons and light waves.•This can only occur if light consists of individual units called “PHOTONS” .•A Photon is a packet of light of discrete energy.•http://www.youtube.com/watch?v=N7BywkIretM&feature=relatedPhotoelectric Effect156.3 Atomic Line Spectra and Niels BohrAn emission spectrum is formed by an electric current passing through a gas in a vacuum tube (at very low pressure) which causes the gas to emit light.–Sometimes called a bright line spectrum.16When the light from a discharge tube containing a pure element (hydrogen in this case) is passed through the same prism, only certain colors (lines) are observed. Recall that color (wavelength) is related to energy via Planck’s law. Light emitted by H2. Emission spectrum of hydrogen.17•An absorption spectrum is formed by shining a beam of white light through a sample of gas.–Absorption spectra indicate the wavelengths of light that have been absorbed.18•Every element has a unique spectrum. •Thus we can use spectra to identify elements.-This can be done in the lab, stars, fireworks, etc.•Spectra can serve as fingerprints that allow us to identify different elements present in a sample, even in trace amounts.19Balmer equation•The Balmer equation is an empirical equation that relates the wavelengths of the lines in the hydrogen spectrum. Derived from numerous observations, not from theory.hydrogen of spectrumemission in the levelsenergy theof numbers therefer to sn’ n n m 10 1.097 Rconstant Rydberg theis R n1n1R 121 1-7222120What is the wavelength of light emitted when the hydrogen atom’s energy changes from n = 4 to n = 2?21Solution: What is the wavelength of light emitted when the hydrogen atom’s energy changes from n = 4 to n = 2?( )( )2 12 21 27 -1 2 27 -1 7 -1 7 -1 6 -1 n 4 and n 21 1 1 R n n1 1 1 1.097 10 m2 41 1 1 1.097 10 m4 161 1.097 10 m 0.250 0.06251 1.097 10 m 0.18751 2.057 10 mllllll= =� �= -� �� �� �= � -� �� �� �= � -� �� �= � -= �= �22Notice that the wavelength calculated from the


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UGA CHEM 1211 - Chapter 6

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