- Principles of Chemistry I: Honors
Fall 2017, Unique 50135
Lecture Summary, 21 September 2017
We briefly reviewed reviewed the basics of waves: waves are
disturbances that propagate through space and time that transfer
energy from one point to another but without causing a permanent
change in the position of any mass. They are described by a
wavelength and an amplitude about an undisturbed state.
Places where amplitude is zero are called nodes.
The frequency of a wave is described by the number of observed
peaks in one second, which is given the unit s-1, or
Hz. The speed of the wave is always equal to its wavelength
times its frequency. For light waves, the speed of light in
a vacuum is 3.0 x 108 m/s.
Development of quantum mechanics: We discussed the state of physics at the end of the 19th century,and the accumulated experimental evidence that indicated that something major was missing from the current understanding of physics (now called"classical" physics). Three major problems that could not be explained at the time were:
1. The existence of a stable atom
2. Blackbody radiation
3. The photoelectric effect
In 1901, Max Planck attempted to deal with these problems by introducing that idea that energy is quantized, or that it comes in discrete packets, not spread out over a continuum. This is a concept which is completely at odds with classical mechanics, but it seemed to describe experimental data of blackbody radiation and the photoelectric effect. Planck did not describe why energy was quantized, nor was he able to explain the stable atom. That remains for our future.