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Unformatted text preview: 1 Electronic Structure Electronic Structure of the Atom of the Atom An Introduction Chapter 7 Note, a major change in direction Note, a major change in direction We are now shifting from numbers and stoichiometry to the particular level. Chapter 7-10 deal with atoms and molecules. We are learning to predict how they will behave. We will also learn several new ways to predict delta H. H. We will see less calculator problems and more definitions Why do we learn Quantum Chemistry? Why do we learn Quantum Chemistry? Classic chemistry cant explain observed light spectra Quantum chemistry can explain light spectra and the photoelectric effect Quantum chemistry can explain periodic trends Nuclear chemistry requires some understanding of quantum chemistry Semiconductors are now reaching quantum chemistry limits. Understanding them takes quantum chemistry. Electromagnetic Radiation Electromagnetic Radiation Visible light is energy. It is one form of Electromagnetic (EM) Radiation . The electromagnetic The electromagnetic spectrum includes many different classifications of radiation, including gamma rays, UV rays, microwaves, and radio waves. Wavelength ( ) The distance from one wave t t th t t Diff t l f li ht z Light exhibits the Light exhibits the properties of waves. properties of waves. Consider a wave: Consider a wave: crest to the next wave crest. Different colors of light have different wavelengths. Frequency ( ) The number of wave cycles that pass a fixed point in a given period of time. Frequency is usually measured in cycles per second (1/s) which is also called Hertz. Frequency, amplitude, wavelength Frequency, amplitude, wavelength 2 Particles and waves act differently Particles and waves act differently Figur Figur e 7.5 e 7.5 The diffraction pattern caused by light The diffraction pattern caused by light passing through two adjacent slits (its waves) . passing through two adjacent slits (its waves) . All EM radiation travels at the speed of light, c = 3.00 x 10 8 m/s (2.99792 x 10 8 m/s). Wavelength and frequency are related by the speed of light: c = The speed of light ( c c ) is a constant; therefore, wavelength and the frequency are inversely wavelength and the frequency are inversely proportional: as the wavelength increases, the frequency decreases. Long wavelength small frequency Short wavelength high frequency Wave Calculations: Wave Calculations: Frequency is measured in: cycles/second = 1/s = s cycles/second = 1/s = s-1 = Hertz = Hz = Hertz = Hz or some multiple ( eg. kHz or MHz) Wavelength is measured in meters (m) meters (m) or some multiple ( eg....
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