Che 131 Notes Ch. 7

Che 131 Notes Ch. 7 - Che 131 Notes Chapter 7 Electron...

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Che 131 Notes Chapter 7: Electron Configurations and the Periodic Table Lecture 10: Radiation and Quantum Theory Reading: 7.1-7.2 I. Atoms contain electrons explanation of periodic trends in physical and chemical properties based on electron configuration A. Electrons arranged in energy levels, a.k.a. shells 1. energies of electrons 2. electrons in outermost shell: valence electrons a. number and location are the chief factors that determine chemical reactivity II. 7.1 Electromagnetic Radiation and Matter A. electromagnetic radiation : oscillating perpendicular electric and magnetic fields that travel through space at the same rate (2.998 x 10 8 m/s) 1. atoms gain energy by absorbing light and become “excited” a. the energy is absorbed by electrons, then released in the form of electromagnetic radiation B. v λ = c 1. frequency (ν): number of complete waves passing a point in a given period of time, or cycles per second, or per second: 1/s a. hertz (Hz) 2. wavelength (λ): distance between adjacent crests (or troughs) in a wave a. meters i. pm: γ (gamma) rays; Å (angstrom) 10 -10 : X rays; nm: ultraviolet & visible; b. inversely related to frequency: as frequency increases, wavelength decreases C. amplitude : height of the wave crest 1. related to intensity of wavelength (i.e. brightness for visible light) a. higher amplitude = more intense radiation D. spectrum : distribution of intensities of wavelengths or frequencies of electromagnetic radiation emitted or absorbed by an object III. 7.2 Planck’s Quantum Theory A. laws of classical physics 1. vibrating atoms in a hot wire causes the emission of electromagnetic vibrations (light waves) – late 19 th century 2. light waves could have any frequency along a continuously varying range a. scientists were unable to predict the experimentally observed spectrum B. 1900 Max Planck: when an atom in a hot object emits radiation, it does so only in packets having a minimum amount of energy 1. there must be a small packet of energy such that no smaller quantity can be emitted (like an atom is the smallest packet of an element) a. quantum : the packet of energy 2. the energy of a quantum is proportional to the frequency of the radiation a. E quantum = radiation b. Planck’s constant : h = 6.626 x 10 -34 J · s
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i. Frequency of radiation to its energy per quantum 3. quantum theory : theory based on Planck’s work a. E = ( hc / λ) i. Energy and wavelength are inversely proportional The energy per quantum of radiation increases as the wavelength gets shorter C. Photoelectric effect : certain metals emit electrons when illuminated by light of certain wavelengths 1. for each photosensitive metal there is a threshold wavelength below which no photoelectric effect is observed a. i.e. Cs emits electrons when illuminated by red light, other metals w/ other colors, ultraviolet light, etc. b.
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This note was uploaded on 10/13/2008 for the course CHE 131 taught by Professor Kerber during the Fall '08 term at SUNY Stony Brook.

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Che 131 Notes Ch. 7 - Che 131 Notes Chapter 7 Electron...

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