plate to collect and interpret these data.
THE WAVE-MECHANICAL MODEL
In the early 1920s, some difficulties with the Bohr model of the atom were
becoming apparent. Although Bohr used classical mechanics (which is the branch
of physics that deals with the motion of bodies under the influence of forces) to
calculate the orbits of the hydrogen atom, this discipline did not serve to explain
the ability of electrons to stay in only certain energy levels without the loss of
energy. Nor could it explain why a change of energy occurred only when an
electron “jumped” from one energy level to another and why the electron could
not exist in the atom at any energy level between these levels. According to
Newton’s laws, the kinetic energy of a body always changes smoothly and
continuously, not in sudden jumps. The idea of only certain quantized energy
levels being available in the Bohr atom was a very important one. The energy
levels explained the existence of atomic spectra, described in the preceding
sections.
Another difficulty with the Bohr model was that it worked well only for the
hydrogen atom with its single electron. It did not work with atoms that had more
electrons. A new approach to the laws governing the behavior of electrons inside
the atom was needed, and such an approach was developed in the 1920s by the
combined work of many scientists. Their work dealt with a more mathematical
model usually referred to as quantum mechanics or wave mechanics. By this
time, Albert Einstein had already proposed a relativity mechanics model to deal
with the relative nature of mass as its speed approaches the speed of light. In the
same manner, a quantum/wave mechanics model was now needed to fit the data of
the atomic model. Max Planck suggested in his quantum theory of light that light
has both particlelike properties and wavelike characteristics. In 1924, Louis de
Broglie, a young French physicist, suggested that, if light can have both wavelike
and particlelike characteristics as Planck had suggested, then perhaps particles
can also have wavelike characteristics. In 1927, de Broglie’s ideas were verified
experimentally when investigators showed that electrons could produce
diffraction patterns, a property associated with waves. Diffraction patterns are
produced by waves as they pass through small holes or narrow slits.
TIP
Know the uncertainty principle.In 1927, Werner Heisenberg stated what is now called the uncertainty
principle. This principle states that it is impossible to know both the precise
location and precise velocity of a subatomic particle at the same time.