http://www.ck12.orgCHAPTER
(^23) The Atom
Chapter Outline
23.1 The Bohr Model of the Atom
23.2 THEQUANTUMMECHANICALMODEL OF THEATOM
23.3 Lasers
23.4 REFERENCES
Illustrated above is a spectrum tube containing helium and the light stripes to the right are the individual frequencies
of light emitted by helium atoms. The color of the tube is the result of the eye mixing all the individual frequencies
together.
When electric current is passed through a tube filled with the gaseous atoms of an individual element, light is
emitted. In the illustration above, the pinkish-yellow colored tube on the left is a tube filled with gaseous helium,
which has electric current passing through. When the light from this tube is passed through a prism, the light is
separated into the individual frequencies that compose it. The spectrum of light from helium atoms contains around
9 separate frequencies.
All helium samples emit exactly the same frequencies when excited. The frequencies emitted by the various
elements are so specific that the spectra can be used to identify the element involved. It was these emissions of
specific frequencies from atoms that led to Bohr’s Model of the Atom and the Quantum Theory Model of the Atom
that followed.
In this unit, you will learn the historical development of the model of the atom.