Chapter 6 - Electronic Structure of Atoms

Chapter 6 - Electronic Structure of Atoms - Chapter 6:...

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1 Chapter 6: Chapter 6: Electronic Structure Electronic Structure of Atoms of Atoms Waves Waves • To understand the electronic structure of atoms, one must understand the nature of electromagnetic radiation. • The distance between corresponding points on adjacent waves is the wavelength ( λ ) .
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2 Waves Waves • The number of waves passing a given point per unit of time is the frequency ( ν ) . • For waves traveling at the same velocity, the longer the wavelength, the smaller the frequency. Electromagnetic Radiation Electromagnetic Radiation • All electromagnetic radiation travels at the same velocity in a vacuum: the speed of light ( c ), c = 3.00 × 10 8 m/s . • The speed of a wave is the product of its wavelength ( λ ) and frequency ( ). c = λν • If either the wavelength or frequency is known, the other can be calculated.
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3 The Nature of Energy The Nature of Energy • The wave nature of light does not explain how an object can glow when its temperature increases. • Max Planck explained it by assuming that energy comes in packets called quanta . •The se quan ta we re assumed to be absorbed or emitted by matter. The Nature of Energy The Nature of Energy • Einstein used this assumption to explain the photoelectric effect. • He concluded that energy is proportional to frequency: E = h ν where h is Planck’s constant, 6.63 × 10 34 J·s. PhotoelectricEffect.MOV
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4 The Nature of Energy The Nature of Energy • Therefore, if one knows the wavelength of light, one can calculate the energy in one photon, or packet, of that light: c = λν E = h ν The Nature of Energy The Nature of Energy Another mystery involved the emission spectra observed from energy emitted by atoms and molecules.
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5 The Nature of Energy The Nature of Energy •One does no t observe a continuous spectrum, as one gets from a white light source. •On ly a line spectrum of discrete wavelengths is observed. The Nature of Energy The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: 1. Electrons in an atom can only occupy certain orbits (corresponding to certain energies).
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6 The Nature of Energy The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: 2. Electrons in permitted orbits have specific, “allowed” energies; these energies will not be radiated from the atom. The Nature of Energy The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: 3. Energy is only absorbed or emitted in such a way as to move an electron from one “allowed” energy state to another; the energy is defined by E = h ν
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7 The Nature of Energy The Nature of Energy The energy absorbed or emitted from the process of electron promotion or demotion can be calculated by the equation: Δ E = R H ( ) 1 n f 2 1 n i 2 - where R H is the Rydberg constant, 2.18 × 10 18 J, and n i and n f are the initial and final energy levels of the electron.
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Chapter 6 - Electronic Structure of Atoms - Chapter 6:...

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