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15 Early Quantum Theory: A Summary
The first quarter of the twentieth century was a perplexing mix of discovery and
wonderment as physicists progressed from the seemingly irrational quantization of
energy by Max Planck (1900) to the inevitability of Werner Heisenberg’s uncertainty
principle (1925). For brevity, we shall refer the reader to more detailed works for
the early history of quantum theory (especially Barrow, 1996; Laidler and Meiser,
1999; Atkins, 1998) and take as our starting point the observations by Louis de
Broglie that small particles—in particular, electrons—have a wave nature and by
Erwin Schrodinger that the spectrum of atomic hydrogen can be deduced by solving ̈
the wave equation that now bears his name.15.1 THE HYDROGEN SPECTRUM
Some substances give off colors in the visible region of the electromagnetic spectrum
when excited by an energy input. An example is sodium, which glows orange when a
solution of NaCl is sprayed into a flame. In general, a multiplicity of distinct energy
levels within an atom leads to a corresponding multiplicity of wavelengths charac-
terized by its uniqueelectromagnetic spectrum. Distinct colors or, more specifically,
wavelengths, are given off or taken up by electrons as they emit or absorb energy of
frequencyνby changing levels. Emitted radiation of different wavelengths can be
separated and recorded in the form of aline spectrum. In most cases, the result of all
these energy exchanges is of bewildering complexity, but one spectrum—that of theConcise Physical Chemistry,by Donald W. Rogers
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