Atomic Spectra

 

 

 

Atomic Spectra

 

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Atomic Spectra

  • When atoms absorb energy, electrons move into higher energy levels, and these electrons lose energy by emitting light when they return to lower energy levels
  • However, the light emitted by atoms consists of a mixture of only specific frequencies
    • Each specific frequency of light corresponds to a particular color
  • Atomic emission spectrum: the pattern formed when light passes through a prism or diffraction grating to separate it into the different frequencies of light it contains
    • Each discrete line in an emission spectrum corresponds to one exact frequency of light emitted by the atom        
  • No two elements have the same emission spectrum
  • Emission spectra are useful for identifying elements

 

An Explanation of Atomic Spectra

  • Bohr’s model explained why the emission spectrum of hydrogen consists of specific frequencies of light and predicted specific values of these frequencies
  • Ground state = the lowest possible energy of the electron
    • It’s when n = 1
  • Excited states: n=2,3,4,5, or 6, etc.

 

Electron transitions

  • electrons can go up to a higher level if energy is absorbed
    • electrons can go down to a lower level if energy is released by emitting light or heat
  • Orbitals have very specific energies
  • Electron transitions involve very specific energy changes and very specific frequencies of light
  • Energy change (Joules) = Planks constant (=6.626 X 10-34 J*s) * frequency (1/s)

                     E = h * ν

  • Energy change and frequency are proportional
    • As energy goes up, frequency goes up

 

  • Lyman series- lines at the ultraviolet end of the hydrogen spectrum
    • higher energy levels to n=1
  • Balmer series- lines in the visible spectrum
    • higher energy levels to n=2
    • energy changes and frequencies of light are both lower
  • Paschen series- lines in the infrared spectrum
    • higher energy levels to n=3
    • These spectral lines became closer together at increased values of n

 

  • PROBLEM: Bohr’s theory explained the emission spectrum of hydrogen, but not the emission spectra of atoms with more than one electron
    • The quantum mechanical model displaced the Bohr model of the atom

 

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Atomic Spectra

 

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Atomic Spectra