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Ch 7: Quantum Theory and Atomic Structure

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University of Alberta
Yoram Apelblat

Silberberg: 5 ed. 7: Quantum Theory & Atomic Structure 7.1 The Nature of Light  EMR = electromagnetic radiation Wave Nature of Light  Frequency (ν) – cycles/ second (aka “hertz” = Hz)  Wavelength (λ) – distance from one crest/trough to the next crest/trough (in meters/nm, etc.) *frequency + wavelength inversely proportional  Speed of light (c) – 2.9979E8 m/s o (ν) x (λ) = c  Amplitude – height of crest/ depth of trough o Related to intensity o Lower amplitude = dimmer/ higher amp. = brighter Know how: to convert frequency wavelength  Refraction –change of speed as light wave travels through different mediums  Diffraction – waves bending around an object o Ex: light wave passing through slits = constructive interference (in phase/bright spot), destructive interference (out of phase/ dark spot) Particle Nature of Light  1900 – Planck’s constant o Proposed that blackbodies could only emit/absorb certain quantities of energy  E =nhv  E = energy v = frequency h = Planck’s constant = 6.626E-34 J/s  Energy gained/lost in “packets” (quantum) o Δ E = E = Δ nhv atom emitted/absorbed  Photoelectric effect not explained by wave model o Presence of threshold frequency: minimum frequency needed for a current o Absence of a time lag: current flows immediately once minimum threshold frequency met  Sometime after Planck – Einstein’s photon theory o Ephotonhv = ΔEatom o Explains threshold frequency: photon of minim. Energy needs to be absorbed in order to free an electron o Explains time lag: brighter light = more photons = faster current once absorbed one photon of enough energy *Know how to: calculate energy of radiation from its wavelengths (and vice versa) 7.2 Atomic Spectra  Rydberg equation predicts position and wavelength of any line in a given series o o R = Rydberg constant = 1.096776E7 m/s *Know how to: use Rydberg equation Bohr Model of the Hydrogen Atom  Explains that energy within an atom only exists in states/ certain discrete levels  Lower n value = smaller radius of orbit = lower energy level o n=1 -> ground state o n=2,3,etc. -> excited state (n=2 = first excited state) o n= ∞ -> ionized Tools of the Lab: Spectrophotometry in Chemical Analysis Spectrophotometry  instrumental techniques that measure concentration o
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