Chem Notes 2nd half

Chem Notes 2nd half - October 10, 2007 Chapter 6 Electronic...

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October 10, 2007 Chapter 6 Electronic Structure of Atoms 6.1 Nature of an atom - What is the nature of an atom ? - Does an atom have parts , if so what are they? - To better understand the nature of an atom we need to understand the “ atomic Structure - A radical new theory called “ Quantum Mechanics ” was developed to account for the behavior of “ light and atom Electromagnetic Radiation - How does energy travel? - Example: Sun, Microwave oven, X-rays, radiant heat from a fire place. - “They all have “ wave-like ” behavior and travel at the speed of light .” Waves - Wavelength- The distance between two consecutive peaks - Wavelength, (λ) Lambda. - 4 cycles/second = 4 hertz (Hz) - The number of waves passing a given point per unit of time is the frequency (ν) (Nu) - All electromagnetic radiation travels at the speed of light (c)= 3.00 x 10 8 m/s - Speed of light = wavelength x frequency - All visible light is electromagnetic radiation , not all electromagnetic radiation is visible light . 6.2 Quantized Energy and Photons Wave model cannot explain many aspects of its behavior: a) Emission of light from hot objects known as ( blackbody radiation ) b) Emission of electron from metal surface ( Photoelectric Effect )
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c) Emission of light from electronically excited gas atoms ( Emission Spectra ) A. Quantization of Energy or Hot Objects a. Wave nature of light does not explain how an object can glow when its temperature increases. b. Max Planck explained it by assuming that energy comes in “ packets ” called quanta c. Energy can only be gained or lost in a whole number October 12, 2007 Quantization of Energy (Blackbody Radiation) - ΔE = n.h.ν o Where n is the energy and h = 6.626 x 10 -34 J.s (Planck constant) - Energy can only be released or absorbed in “discrete chunks.” Therefore, ΔE is not continuous but “quantitized” - Each of these packets “hν” of energy Photoelectric effect and photons emission of e- from Metal Surfaces - If one knows the wavelength of light, one can calculate the energy in one photon, or packet. Therefore electromagnetic radiation is itself quantitized. E photon = hν c = λν 6.3 Line Spectra and the Bohr Model - Another mystery involved the emission spectra observed from energy emitted by atoms and molecules. - Radiation composed of a single wavelength is said to be Monochromatic - Most radiation sources produced many different wavelengths called spectrum . The Nature of Energy The energy absorbed or emitted from the process of electron promotion or demotion can be calculated by the equation: written equation Where R H is the Rydberg constant, -2.18 x 10 -18 J and n i Quantum Mechanics (Model drawn in notes)
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- The wave equation is designated with a lower case Greek psi (ψ) Quantum Numbers o Solving the wave equation gives a set of wave functions, or orbitals , and their corresponding energies. o
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Chem Notes 2nd half - October 10, 2007 Chapter 6 Electronic...

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