I Chapter 6 A Light Versus Matter 1 Light a Continuum of...

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I. Chapter 6 A. Light Versus Matter 1. Light a) Continuum of radiant energies b) Massless c) No definite position d) waves 2. Matter a) Discrete b) Fixed mass c) Fixed position d) Particles B. Describing Waves 1. Frequency (v, s -1 , Hz) a) Number of cycles a wave undergoes per second 2. Wavelength a) Distance a wave travels in one full cycle 3. Speed of light © a) c =λv 4. Amplitude = intensity of a wave C. The electromagnetic spectrum 1. Varying wavelengths 2. → increasing wavelength 3. ← increasing frequency 4. ← increasing energy D. Electromagnetic Radiation 1. C = 3.00x10 8 m/s - speed of light in a vacuum 2. h=626x10 -34 Js - Planck’s constant E. Waves Versus Particles 1. Refraction a) Waves bends the length and changes the angle b) Particles do not 2. Diffraction a) Sound going through small hole in waves b) Versus beam going straight through 3. Light a) Particle nature (1) Classical physics stated that light was a wave (a) Refraction in different media, diffraction patterns b) Particle behavior (1) Blackbody radiation (a) Heating an object increases its KE and emits light (b) Classical: amounts of energy being released by objects hot as the sun
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(c) This did not match observations where a max. Emission intensity occurs (d) Planck proposed that atoms could only vibrate at whole integer (quantized) values (i) New equation: E=nhv (ii) n= integers (iii) h=planck's constant (2) Photoelectric effect (a) Under proper conditions, it was observed that light could knock electrons free from metal plates (b) Each metal was found to have a discrete threshold frequency for the light, below which electrons would not be ejected (c) The KE (Speed) of the ejected electrons depended on the frequency of the light, not the amplitude (brightness) (d) Einstein proposed that light hitting the metal shouldn’t be viewed as a wave, rather a stream of particles (photons) (e) The energy of the photon depends on their frequency (f) E photon = +E ϴ Kinetic (g) = work function ϴ (h) E Kinetic = max KE of electron (3) The emission of light from hot elements (a) Heating a solid, liquid, or condensed gas to high enough temps will result in a continuous emission spectrum (b) Heating gases at how pressures results in discrete emission spectra (line spectra) (c) Hydrogen line spectra (i) The line spectrum for hydrogen atoms was found to be empirically solvable (ii) The Rydberg equation predicts all the emission lines from hydrogen atoms (a) 1/λ=R (1/n 1 2 -1/n 2 2 ) (iii) Bohr Model (a) Postulates that the electron orbiting the hydrogen could only be at fixed distances from the nucleus
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(b) The transition of the electron from one orbit to another would release or absorb energy (c) ΔE=2.18x10 -18 J[(1/n I 2 )-(1/n F 2 )] (d) Electron energy (i) Bohr can be applied to calculate the energy of single electron in a specific orbit around the nucleus (ii) Works for all hydrogenic atoms (single electron) (iii) ΔE=-2.18x10 -18 J[(Z 2 /n 2 ))] (iv) ΔE=2.18x10 -18 J[(Z 2 /n I 2 )- (Z 2 /n F 2 )] c)
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