HCC CHEM 161 - Electronic Structure
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Chapter 7: Electronic StructureLightElectromagnetic RadiationLight as a WaveSlide 5Electromagnetic SpectrumSlide 7Proof of WavesSlide 9Slide 10Light as a ParticleSlide 12Slide 13Line SpectraSlide 15High Voltage ExcitationIdentifying MetalsSlide 18Bohr TheorySlide 20Slide 21Slide 22Matter as a WaveSlide 24Uncertainty PrincipleSlide 26Slide 27Slide 28Slide 29Slide 30Slide 31Quantum MechanicsHy = EyAtomic OrbitalsSlide 35Slide 36Slide 37Slide 38Slide 39Quantum NumbersSlide 41Slide 42Slide 43Slide 44Slide 45Subshell DesignationsOrbitalsSlide 48Slide 49Chapter 7: Electronic Chapter 7: Electronic StructureStructureElectrons in an atom determine virtually all of the behavior of the atom.Quantum theory – the study of how energy and matter interact on an atomic level.To understand the electron, we must first understand light.Reason =LightLightAlso known as electromagnetic radiation.Ex) Visible light, Infrared, X-ray, Radio.All electromagnetic radiation have several common characteristics.◦Light as a wave◦Light as a particle◦“Duality of Light”Electromagnetic RadiationElectromagnetic RadiationLight as a WaveLight as a WaveWavelength ( – lambda) = Frequency ( – nu) =Light as a WaveLight as a Wave•Wavelength and Frequency are inversely related.Electromagnetic SpectrumElectromagnetic SpectrumShows the full range of electromagnetic radiation that exists.Light as a WaveLight as a WaveThe product of the wavelength and the frequency, though, is a constant.c =  , where c is the speed of light.Thus, if we know the frequency, we can find the wavelength and vice versa.LEP #1(a).Proof of WavesProof of WavesWaves exhibit certain properties when they interact with each other.Young’s Double Slit experiment.Proof of WavesProof of WavesProof of WavesProof of WavesLight as a ParticleLight as a ParticleThe wave nature of light does not explain all of the properties of light.Blackbody radiation – when solids are heated, they will glow.Color depends on the temperature.Light as a ParticleLight as a ParticleMax Planck – proposed a theory that energy from blackbody radiation could only come in discrete “chunks” or quanta.E = h h = 6.626 x 10-34 J-sLEP #1(b).Light as a ParticleLight as a ParticleThe photoelectric effect (Einstein) also is proof that light must have a tiny mass and thus act as a particle (photon).LEP #2, #3.Line SpectraLine SpectraWhen a gas like H2, Hg, or He is subjected to a high voltage, it produces a line spectrum consisting of specific wavelengths.Line SpectraLine SpectraHigh Voltage ExcitationHigh Voltage ExcitationIdentifying MetalsIdentifying Metals Na = yellow K = violet Li = red Ba = pale greenLine SpectraLine SpectraThe four lines for hydrogen were found to follow the formula:Where the values of n are integers with the final state being the smaller integer.( )72 2f i1 1 1 = 1.097 10 / m - λ n n� ��� �� �Bohr TheoryBohr TheoryHow could such a simple equation work?Niels Bohr some thirty years later came up with a theory.Classic physics would predict that an electron in a circular path should continuously lose energy until it spiraled into the nucleus.Bohr TheoryBohr Theory1. An electron can only have precise energies according to the formula: E = -RH / n2 ; n = 1, 2, 3, etc. and RH is the Rydberg constant.2. An electron can travel between energy states by absorbing or releasing a precise quantity of energy.Bohr TheoryBohr TheoryBohr TheoryBohr TheoryCan not explain the line spectra for other elements due to electron-electron interactions.Thus, the formula for Hydrogen can only be applied for that atom.LEP #4.Matter as a WaveMatter as a WaveLouis de Broglie proposed that if light could act as both a wave and a particle, then so could matter.Where h is Planck’s constant, m is the objects mass, and v is its velocity.Size, though, matters. LEP #5.hλ = mvMatter as a WaveMatter as a WaveDe Broglie was later proven correct when electrons were shown to have wave properties when they pass through a crystalline substance.Electron microscope picture of carbon nanotubes.Uncertainty PrincipleUncertainty PrincipleGerman scientist Werner Heisenberg proposed his Uncertainty Principle in 1927.HistoryUncertainty PrincipleUncertainty PrincipleFor a projectile like a bullet, classic physics has formulas to describe the motion – velocity and position – as it travels down range.Uncertainty PrincipleUncertainty PrincipleAny attempt to observe a single electron will fail.Uncertainty PrincipleUncertainty PrincipleIf you want to measure length, there is always some uncertainty in the measurement.To improve the certainty, you would make a better measuring device.Heisenberg, though, stated that the precision has limitations.x - mv  h / 4Uncertainty PrincipleUncertainty PrincipleOnce again, size makes a big difference.LEP #6Uncertainty PrincipleUncertainty PrincipleDeterminacy vs. IndeterminacyAccording to classical physics, particles move in a path determined by the particle’s velocity, position, and forces acting on it◦determinacy = definite, predictable futureBecause we cannot know both the position and velocity of an electron, we cannot predict the path it will follow◦indeterminacy = indefinite future, can only predict probabilityUncertainty PrincipleUncertainty PrincipleQuantum MechanicsQuantum MechanicsThe quantum world is very different from the ordinary world.Millions of possible outcomes and all are possible!Quantum Café“I am convinced that He (God) does not play dice.” Albert EinsteinHH = E = EErwin Shrödinger proposed an equation that describes both the wave and particle behavior of an electron.The mathematical function, , describes the wave form of the electron. Ex) a sine wave.Squaring this function produces a probability function for our electron.Atomic OrbitalsAtomic OrbitalsA graph of 2 versus the radial distance from the nucleus yields an electron “orbital”.An “orbital” is a 3D shape of where an electron is most of the time.An “orbital” can hold a maximum of two electrons.Atomic OrbitalsAtomic OrbitalsThe Probability density function represents the probability of finding the electron.Atomic OrbitalsAtomic Orbitals•A radial distribution plot represents the total probability


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HCC CHEM 161 - Electronic Structure

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