1814 - Joseph von Fraunhofer

• Studied the absorption spectrum of the light given off by the sun.
  • Absorption Spectrum - The spectrum of dark lines against a light background that results from the absorption of selected frequencies of the electromagnetic radiation by an atom or molecule.

1855-1860 - Robert Bunsen and Gustav Kirchhoff

		Developed a spectroscope that focused the light from a burner flame onto a prism that separated the light into its spectrum.  Studied the emission spectrum of several metals. Emission Spectrum - The spectrum of bright lines against a dark background obtained when an atom or molecule emits radiation when excited by heat or an electric discharge.
Robert Bunsen	Gustav Kirchhoff

Flame Test
The following metals give emit certain colors of light when their atoms are excited.

1885 - Johann Jacob Balmer

Analyzed the hydrogen spectrum and found that hydrogen emitted four bands of light within the visible spectrum: Wavelength (nm)     Color 656.2 red 486.1 blue 434.0 blue-violet 410.1 violet

• Balmer found that the data fit to the following equation:

• = wavelength (nm)

• R_H = Rydberg's constant = 1.09678 x 10^-2 nm^-1

• n₁ = the lower energy level

• n₂ = the higher energy level

For example, to calculate the wavelength of light emitted when the electron in a hydrogen atom falls from the fourth energy level to the second energy level:

Each series is named after its discoverer. The Lyman series is the wavelengths in the ultra violet (UV) spectrum of the hydrogen atom, resulting from electrons dropping from higher energy levels into the n = 1 orbit. The Balmer series is the wavelengths in the visible light spectrum of the hydrogen atom, resulting from electrons falling from higher energy levels into the n = 2 orbit. The Paschen series is the wavelengths in the infrared spectrum of the hydrogen atom, resulting from electrons falling from higher energy levels into the n = 3 orbit. The Brackett series is the wavelengths in the infrared spectrum of the hydrogen atom, resulting from electrons falling from higher energy levels into the n = 4 orbit. The Pfund series is the wavelengths in the infrared spectrum of the hydrogen atom, resulting from electrons falling from higher energy levels into the n = 5 orbit.

1900 - Max Planck

Hypothesized that substances were surrounded by oscillating "resonators" which emitted energy that was quantized, or countable, because he assumed that there were only a limited number of energies at which these oscillators could exist.

1905 - Albert Einstein

• Extended Planck's work to include light, hypothesizing that light was also quantized.
• He assumed that:
  1. Light was made up of small, discrete particles of energy called photons.
  2. The energy (E) of a photon is proportional to its frequency (v):

     where h is Planck's constant = 6.626 x 10^-34 J-s.

Next:  "Bohr Model"