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chapter7

# chapter7 - Note a major change in direction Electronic...

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1 Electronic Structure of the Atom An Introduction – Chapter 7 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. • We will see less calculator problems and more definitions Why do we learn Quantum Chemistry? Classic chemistry can’t 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 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 ( λ ) The distance from one wave t t th t t Diff t l f li ht z Light exhibits the properties of waves. Consider a wave: crest to the next wave crest. Different colors of light have different wavelengths. Frequency ( ν ) 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

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2 Particles and waves act differently Figur e 7.5 The diffraction pattern caused by light passing through two adjacent slits (it’s 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 = λ ν The speed of light ( 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 Æ small frequency Short wavelength Æ high frequency Wave Calculations: Frequency is measured in: cycles/second = 1/s = s -1 = Hertz = Hz or some multiple ( eg. kHz or MHz) Wavelength is measured in meters (m) meters (m) or some multiple ( eg. nm or μ m). Example problems: 1) What is the frequency of light with a wavelength of 535 nm? 1070 nm? 2) What is the wavelength of a radio broadcasting at 102.1 kHz? The EM spectrum Where do you use EM waves? TV and radio signals are long wavelength (lower energy). Cell phones work in radio waves to microwaves (2 meter long=common) Microwave ovens work at 2.45 GHz, right energy to excite water to vibrate IR: we feel it as heat (causes vibrations=“heats up”) Visible=what we see Ultraviolet: more energetic, causes sunburns X-rays: energetic enough to go through humans, image bones, structures. Can cause damage Gamma rays: kills. High energy, short wavelength

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chapter7 - Note a major change in direction Electronic...

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