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Atomic Structure II (Ch.5)

Atomic Structure II (Ch.5). Introduction: Wave-Particle Nature of Light. Discoveries about the nature of light led to greater understanding of the properties of electrons and atomic structure.

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Atomic Structure II (Ch.5)

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  1. Atomic Structure II (Ch.5) Introduction: Wave-Particle Nature of Light Discoveries about the nature of light led to greater understanding of the properties of electrons and atomic structure.

  2. 1800’s: Electrons were thought of as particles; light was thought of as waves. Experimental observations can support both these theories. Early 1900’s: New experiments showed that electrons have some wave-like properties and light has some particle-like properties. These discoveries led to the ideathat both electrons and light have a dual wave-particle nature. (This was the beginning of quantum physics.)

  3. Light is a form of electromagnetic radiation. A. electromagnetic radiation (EMR)- energy that has wave characteristics as it travels through space.

  4. Visible light is one form of electromagnetic radiation; others include x-rays, ultraviolet light, infrared light, TV and radio waves. Electromagnetic spectrum – consists of all the forms ofEMR arranged in order by wavelength. All types of electromagnetic radiation travel at a speed of 3.00 x 108 m/s. This is called the speed of light (c).

  5. Electromagnetic Spectrum

  6. Waves Waves transfer energy from one place to another B. Electromagnetic radiation has the following wave characteristics:

  7. 1. Wavelength,  (lambda) = distance between successive points 2m 10m

  8. 2. Frequency,  (nu) = the number of waves that pass a given point per unit of time; Cycles per second t=5 t=0 t=0 t=5

  9. Units for Frequency • 1/s • s-1 • hertz, Hz FM Radio stations are identified by their frequency in MHz. ; AM Radio stations are identified by their frequency in kHz.

  10. 3. Wave Velocity • Velocity of a wave (m/s) = wavelength (m) x frequency (1/s) • c =  • 3.00x108 m/s = 

  11. Because all electromagnetic waves travel at the speed of light, wavelength is determined by frequency: Low frequency = long wavelengths High frequency = short wavelengths Wavelength and frequency are inversely proportional.

  12. The yellow light given off by a sodium vapor light • has a wavelength of 589 nm. What is the lights frequency? 2. A laser used to fuse detached retinas has radiation witha frequency of 4.7 x 1014 Hz. What is its wavelength in nm?

  13. 3. Calculate the wavelength (in nm) of a microwave that hasthe frequency of 3.25 x 1010 Hz. 9.23 x 106 nm 4. What is the frequency of blue light that has a wavelength of 475 nm? 6.31 x 1014 Hz

  14. 1. An x-ray has a frequency of 2.5 x 1018 Hz. What is the wavelength of the x-ray? 2. A red light has a wavelength of 725 nm. What is the frequency of the red light?

  15. C. Prisms A prism can be used to “spread out” the wavelengths of light.

  16. Continuous spectrum – a spectrum in which all the wavelengths within a given range are included. A rainbow would be an example of a continuous spectrum of visible light.

  17. D. Light shows the wave property of Interference. (Physics 2000 – Interference Experiments)

  18. II. Light as a Particle two properties of light could not be explained in terms of waves: A) emission of light by hot objects; B) the photoelectric effect.

  19. A. (1900) Max Planck says energy can only be released or absorbed by atoms in "packets of energy" called quanta. The energy of a quantum (E) is given by the equation:E = h = frequency; h = Planck's constant: 6.63 x 10-34 Js EX: Calculate the energy of a quantum of radiation whose frequency is 3.0 x 1011 Hz.

  20. Higher-frequency electromagnetic waves have higher energy than lower-frequency electromagnetic waves • All forms of electromagnetic energy interact with matter, and the ability of these different waves to penetrate matter is a measure of the energy of the waves

  21. B. Photoelectric Effect - the phenomena whereby a metal will emit electrons if light with a certain minimum frequency is shined on it. Photoelectric Effect Animation

  22. (1905) Einstein explains photoelectric effect by saying that light consists of quanta. Only if the light has a high enough frequency will the quanta have enough energy to dislodge an electron. Einstein called these quanta or "particles" of light photons. Light (and all electromagnetic radiation) has both wave-like and particle like properties.

  23. EX Problem 1: A purple light has a frequency of 7.5 x 1014 Hz. What is the energy of a photon of purple light? 5.0 x 10-19 J EX2: A green light has a wavelength of 500. nm. Calculate the energy of a photon of green light. 3.98 x 10-19 J

  24. A blue light has a frequency of 6.7 x 1014 Hz. Calculate the energy of a photon of blue light. • Radio signals from station WIP have a frequency of 6.1 x 105 s-1. Calculate the energy of a photon of this radio signal. • A yellow light has a wavelength of 575 nm. Calculate the energy of a photon of this light. 4.4 x 10-19 J 4.0 x 10-28 J 3.46 x 10-19 J

  25. III. Line Spectra (bright-line spectra, atomic emission spectra) • Line Spectra ( or bright-line spectra) – these lines of color are produced when the light from an element is passed through a prism. • Each element produces a characteristic set of lines called the line spectrum of the element. Elements can be identified by their line spectrum. • Each line in a line spectrum represents a particular wavelength and frequency of light given off. You can calculate the energy of the photons of light using E=h • Bohr used the line spectrum of hydrogen to devise his model of the atom.

  26. III. Line Spectra 2. Line Spectra Animation 1. Physics 2000 – Quantum Atom - Line Spectra

  27. I. Quantum Mechanics A. (1924) Louis de Broglie says if light has a dual wave-particle nature, then matter (electrons) could also have a dual wave-particle nature. Quantum Model of Atom

  28. Electron Interference Animation(Web) Drive Experiments showed that electrons display the wave properties of diffraction and interference.

  29. B. Heisenberg Uncertainty Principle It is impossible to know exactly both the location and velocity of an electron at the same time.

  30. C. Schrodinger Wave Equation Describes the probability of where an electron can be found. Schrodinger’s equation works for all atoms. D. Quantum theory – describes mathematically the wave properties of electrons. In the quantum model of the atom, electrons are found in orbitals, not specific orbits.

  31. Quantum Theory

  32. Orbitals

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