Final Prep Answers

Energy / eV
Chem 155 Final review topics and questions:
22. Light of variable wavelength is incident on a piece of metal in vacuum, the metal
is held at zero volts. Electrons emitted from the metal are collected and analyzed
as a function of energy. Draw a diagram of the photoelectron energy versus the
irradiating light frequency. Identify the x-intercept and the slope of the curve and
indicate the significance of both.
See notes on photoelectric effect: x-intercept is the work function of the metal –
the energy required to take an electron out of the conduction band and into
vacuum. The slope of the line is Plank’s constant.
23. A small hypothetical molecule has the following energy level diagram. Indicate,
using arrows, the transitions corresponding to infrared light absorption, visible
light absorption, and visible light fluorescence. Be prepared to sketch the
absorbance or fluorescence spectra as well.
3
2
1
Vis
abs.
Vis
fluor.
Vis
abs.
Vis
fluor.
0
IR
abs.
400 500 600
Wavelength / nm increasing