GenChem1Chap7

GenChem1Chap7 - 7. Quantum Theory and the Electronic...

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Unformatted text preview: 7. Quantum Theory and the Electronic Structure of Atoms microscopic viewpoint: atoms structure of atom aspect relevant to chemistry: electrons around the nucleus information about the electronic structure: elec tro mag net ic ra- di a tion = wave of electric and magnetic fields wave: transport of energy ( but not matter ); periodic in space and time wavelength [ m] ; amplitude A frequency = number of crests time [ 1/s] 1/s = Hz (hertz) 1 cm = 10- 2 m , 1 m = 10- 6 m , 1 nm = 10- 9 m , 1 = 10- 10 m = c wave speed electromagnetic radiation: B E , B c ; generated by an accel- erating charge c = 2.997925 10 8 m s- 1 speed of light in vacuum GChem I 7.1 visible light: narrow part of electromagnetic radiation spectrum ; = 390 nm (violet) 760 nm (red) yellow-green : 550 nm max: sun, eye sun light, incandescent light bulb: continuous range of frequen- cies (or wavelengths) = con tin u ous spec trum light emitted from certain gaseous substances has only a limited number of colored lines (frequencies or wavelengths) = dis con- tin u ous spec trum line spectrum , atomic spectrum hydrogen lamp: lines in the visible at = 656.3 nm , 468.1 nm , 434.0 nm , 410.1 nm H line spectrum Balmer series = 3.2881 10 15 1 s 1 2 2- 1 n 2 , n = 3,4,... classical physics (pre-1900): lines cannot be explained blackbody radiation : black body = perfect absorber and emitter of radiation; spectrum of heated solids; also cannot be explained by classical physics Planck (1900): energy is discontinuous = energy is quantized GChem I 7.2 there is a smallest, nonzero value for energy differences: quan- tum of energy energy of a system has only a discrete set of values: multiples of the quantum quantum of electromagnetic radiation : E = h h = 6.626 10- 34 Js Plancks constant photoelectric effect : metal e- electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency; if < th , no electrons are ejected number of electrons depends on the light intensity (amplitude), but the energy of an ejected electron does not Einstein (1905): light = stream of particles , photon h GChem I 7.3 Classical physics: Rutherford atom is...
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GenChem1Chap7 - 7. Quantum Theory and the Electronic...

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