Page 146 - Chemistry--atom first

136 Chapter 3 | Electronic Structure and Periodic Properties of Elements
Figure 3.17 If an electron is viewed as a wave circling around the nucleus, an integer number of wavelengths must fit into the orbit for this standing wave behavior to be possible.
For a circular orbit of radius r, the circumference is 2πr, and so de Broglie’s condition is:
Since the de Broglie expression relates the wavelength to the momentum and, hence, velocity, this implies:

This expression can be rearranged to give Bohr’s formula for the quantization of the angular momentum:

Classical angular momentum L for a circular motion is equal to the product of the radius of the circle and the momentum of the moving particle p.

Figure 3.18 The diagram shows angular momentum for a circular motion.
Shortly after de Broglie proposed the wave nature of matter, two scientists at Bell Laboratories, C. J. Davisson and L. H. Germer, demonstrated experimentally that electrons can exhibit wavelike behavior by showing an interference pattern for electrons travelling through a regular atomic pattern in a crystal. The regularly spaced atomic layers served as slits, as used in other interference experiments. Since the spacing between the layers serving as slits needs to be similar in size to the wavelength of the tested wave for an interference pattern to form, Davisson and Germer used a crystalline nickel target for their “slits,” since the spacing of the atoms within the lattice was approximately the same as the de Broglie wavelengths of the electrons that they used. Figure 3.19 shows an interference pattern. It is strikingly similar to the interference patterns for light shown in Figure 3.6. The wave–particle duality of matter can be seen in Figure 3.19 by observing what happens if electron collisions are recorded over a long period of
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