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Spectroscopy

Spectroscopy. Interaction between atoms and light. Source: Wikimedia Commons. Light. Light is the key to understanding the modern atom. Has both wave and particle properties depending on how you measure it. A packet of light is called a photon.

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Spectroscopy

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  1. Spectroscopy Interaction between atoms and light.

  2. Source: Wikimedia Commons Light • Light is the key to understanding the modern atom. • Has both wave and particle properties depending on how you measure it. • A packet of light is called a photon.

  3. Source: North Carolina End-of-Course Chemistry Reference Table • All electromagnetic radiation is light.

  4. Source: library.thinkquest.org, Used by permission Wavelength • Wavelength – λ (lambda) – the distance between two equivalent points on a wave. • Measured in length units, (m, nm, pm, etc.)

  5. Source: Wikimedia Commons Characteristics of Light • Frequency – ν (nu) – the number of times a particular point on a wave passes by an observer in one second. • Measured in Hertz, Hz = 1/s

  6. Source: Wikimedia Commons Relationship Between Frequency and Wavelength • Wavelength and Frequency are Inversely Related • As one goes up the other goes down. • c = λν • c = speed of light = 2.998 x 108 m/s

  7. Characteristics of Light • There are a wide range of frequencies and wavelengths of light.

  8. Characteristics of Light • One photon of light can transfer only a specific amount of energy • The energy of one photon, E = hν • E = energy of one photon • h = Planck’s constant, 6.626 x 10-34 J•s • v = frequency • Energy is proportional to frequency

  9. Source: North Carolina End-of-Course Chemistry Reference Table • Which light can do the most damage to you? • Short wavelength and high frequency has the highest energy

  10. Light • Wavelength and Frequency are inversely related. • Frequency and Energy are directly related. • Wavelength and Energy are inversely related.

  11. Practice Problems • The newly developing LTE cell networks are in the 700MHz band. Verizon’s uplink band starts at 777MHz. What is the wavelength of a photon of this light? • What is the energy of a photon transmitted at 777MHz?

  12. Atomic Spectra • Emission Spectrum • Spectrum of light emitted by a substance when energy is added. • Flame Tests • Discharge Tubes

  13. Atom Emission Spectra

  14. Atom Emission Spectra

  15. Simple Initial Model • Hydrogen Atom • Only one electron • Therefore, quantum mechanical calculations simplify tremendously. • All subshells are degenerate with each other in the same shell. • We can just worry about transitions from one shell to another shell with out caring about what subshell it ends up in.

  16. Source: North Carolina End-of-Course Chemistry Reference Table Specific Energy Levels n = 1,2,3,4, etc. Transition from “excited” state to “ground” state and the light produced by the transition.

  17. Multi-Electron Atoms • Subshells are not all the same energy. • Determining the transitions becomes much harder.

  18. Emission Spectrum • 670nm = 1s22p1 to 1s22s1 • Excited state to ground state • Strongest line and gives lithium flame test its color. • 610nm = 1s23d1 to 1s22p1 • Excited state to lower excited state • 497nm = 1s24s1 to 1s22p1 • Excited state to lower excited state • 460nm = 1s24d1 to 1s22p1 • Excited state to lower excited state

  19. Practice • What is the energy of a photon emitted from a hydrogen atom when an electron jumps from n = 3 to n = 1?

  20. Test Review Problem • In graphite, carbon atoms are about 142pm apart. This distance could be resolved by a system that emitted a wavelength of light roughly half of that distance. What is the frequency and energy of this light?

  21. Test Review Problem • Chlorofluorocarbons, or CFC’s, have been banned from production in the US since 1994. When they are released into the air, they may migrate into the upper atmosphere. In the upper atmosphere, the carbon-chlorine bonds can be broken by a photon of light with energy of 5.45x10-19 J. The free chlorine atom can go on to cause the decomposition of multiple ozone molecules in a catalytic process (and therefore why they are banned). What is the wavelength of light that can cause the bond to break?

  22. Old cordless phones used a 700.0MHz band for communication with the base station. What is the wavelength and energy of a photon of this light?

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