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Isotope characteristics differ U 238 92 U 235 92

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Binding energy Energy released when a nucleus is formed from protons and neutrons. Mass is lost. E = mc 2 –where m is the lost mass

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The photon A “particle” of light A “quantum” of light energy The energy of a given photon depends on the frequency (color) of the light

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But light is also a wave! Travels at constant speed c in a vacuum. c = f –c: 3 x 10 8 m/s – wavelength (m) – f: frequency (Hz)

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Calculating photon energy E = hf –E: energy (J or eV) –h: Planck’s constant 6.625 10 -34 J s or 4.14 10 -15 eV s –f: frequency of light (s -1, Hz)

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The “electron-volt” (eV) is an energy unit Useful on the atomic level. If a moving electron is stopped by 1 V of electric potential, we say it has 1 electron-volt (or 1 eV) of kinetic energy!

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Converting eV to Joules (J) 1 eV = 1.602 10 -19 J

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Absorption Spectrum Photon is absorbed and excites atom to higher quantum energy state. 0 eV -10 eV hf Ground state EE

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Absorption Spectrum Absorption spectra always involve atoms going up in energy level. 0 eV -10 eV ionized

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Emission Spectrum Photon is emitted and atom drops to lower quantum energy state. 0 eV -10 eV hf Excited state EE

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Emission Spectrum Emission spectra always involve atoms going down in energy level. 0 eV -10 eV ionized

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Wavelength Photon – = c/f Particle – = h/p – deBroglie wavelength

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Compton Scattering Proof of the momentum of photons. High-energy photons collided with electrons. Conservation of momentum. Scattered photons examined to determine loss of momentum.

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Davisson-Germer Experiement Verified that electrons have wave properties by proving that they diffract. Electron diffraction

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Preview Objectives Properties of Light Wavelength and Frequency The Photoelectric Effect The Hydrogen-Atom Line-Emission Spectrum Bohr Model of the Hydrogen.

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