Session 1, Page 12: Spectral Lines

Although Kirchoff had discovered the conditions under which the different kinds of spectra were produced, the exact mechanism responsible for the phenomenon remained a mystery until the early 20th century. In 1913 Niels Bohr published his revolutionary model of the atom, the basic building block of matter. His model was based upon the following assumptions:

Electrons exist in stable orbits about the nucleus
Only certain orbits are allowed
An electron passing from a lower orbit to a higher orbit must absorb light with exactly the difference in energy between the two orbits. Similarly, for an electron to move from a higher orbit to a lower one, it must emit light corresponding to exactly the difference in energy.

Bohr's model allowed a simple understanding of the absorption or emission of light by atoms that explained line spectra.

Figure 16
Courtesy University of Oregon

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