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Chapter 7

CHEM UA 125- Chapter 7 Illustrated Notes

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New York University
John Halpin

Chapter 7 NotesAnnotatedAnnotatedAnnotatedpdf15 MBChapter 7 NotesAnnotatedAnnotatedpdf10 MBChapter 7 NotesAnnotatedpdf5428 KBChapter 7 Notespdf571 KB71electromagnetic radiation consists of energy propagated by electric and magnetic fields that increase and decrease in intensity as they move through space this is classical wave modelbut cannot explain observations on the atomic scalefrequency number of cycles it undergoes per second 1s or Hzwavelength the distance between any point on a wave and the corresponding point on the next crest or trough of the wave the distance the wave travels during one cycle mspeed distance it moves per unit time msproduct of frequency and wavelength reciprocal relationship high frequency results in short wavelength etccspeed of light299792458 x 108 msamplitude height of the crest or depth of the troughrelated to the intensity of radiationbrightness of colorthe electro magnetic spectrum a continuum of radiant energyall waves in the spectrum travel at the same speed through a vacuum but differ in frequency and therefore wavelengthhighest to lowest energy Gamma rays xrays ultraviolet visible ROYGBIV infrared microwave radiorefraction when a waves path is immediately changed when the wave passes between mediaex when an object is at a different angle underwater than in the airangle of refraction depends on the two media and the wavelength of the lighta particle can NOT undergo refractiondispersion when white light separates into its component colors when it passes through a refracting object ex prism because each incoming wave is refracted at a slightly different anglediffraction when a wave strikes the edge of an object it bends around it forms a semicircular wave on the other side of the openingparticles not all particles go through the openinginterference when nearby emerging circular waves interactparticles pass through openings straightconstructive crests of the waves coincide in phasedestructive crests coincide with troughs out of phaseresults in a diffraction patternlackbody radiation when a solid object is heated to about 1000 K it begins to emit visible lightnot explainable by classical electromagnetic theory quantum theory the explanation Planck proclaimed that the hot glowing object could emitabsorb only certain quantities of energyEnergy of radiationPlancks constantfrequencyplancks constanth6626 x 10 34 Jsquantum an energy packetan atom changes its energy state by emitting or absorbing one or more quantaan atom has only certain quantities of energy and can only change its energy by absorbingemitting a photon whose energy equals the change in the atoms energyphotoelectric effect when monochromatic light of sufficient frequency shines of an metal plate a current formspresence of threshold frequency and absence of time lag confusesexplanation the photon theory light itself is particulate quanticizd into thing bundles of energies called photons threshold frequency intensity related to number of photons not energy of eachno time lag electron breaks free when it absorbs a photon of enough energy 72line spectrum a series of fine lines at specific frequencies separated by black spacesoccurs when light from electrically excited gaseous atoms pass through a slit and is reflected by a prismeach spectrum is unique to the element producing itRydberg Equation predicts the position and wavelength of any line in a given series1wavelengthR 1n121n22Rutherfords nuclear model didnt explain the line spectraBohrs model accounted for the line spectraBohr model of the hydrogen atomPostulates of the modelH atom has only certain energy levels stationary stateselectrons have a fixed circular orbithigher the energy level the farther the electron is from the nucleusThe atom does not radiate energy while in one of its stationary stateswhile the electron is within orbit the atom doesnt change energyThe atom changes to another stationary state electron moves to another orbit only by absorbing or emitting a photonEnergy of a photonchange in energy of an atomEnergy finalenergy initialhvFeatures of the modelQuantum numbers and electron orbitthe lower the n value the smaller the readies of the orbit and the lower the energy levelground statefirst orbit n1 is called the ground state the electron is closest to the nucleusexcited statewhen the electron is in any orbit farther from the nucleus2nd orbitn2first excited stateabsorptionelectron moves to an outerhigher energy obit if it absorbs a photon whose energy equals the difference b
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