Absorption of electromagnetic energy corresponds to an atom or a molecule gaining energy and going from a lower energy level to a higher energy level.
White light, one type of electromagnetic energy, is composed of all colors of visible light. When
a substance or solution absorbs some wavelengths of white light, the substance or solution has color.
The spectroscope can be used to investigate which wavelengths
of light a sample is absorbing.
Absorption spectrum as seen through a hand-held spectroscope. The back portions of the spectrum are wavelengths of light that have been absorbed by the sample.
All
components of white light that a sample does not absorb are transmitted,
and a color wheel can be used to predict the appearance of the
sample. In general, if one color of light is absorbed, the sample will appear to be the color on the wheel opposite to the one absorbed.
For example, if a sample only absorbs light from 650 nm to
700 nm (red light), all other wavelengths will be transmitted. The sample will appear green, since green is the complementary color to red and is across from red on the color wheel. (Note: A sample may absorb
more than one color, and predicting its appearance becomes more
difficult.)
Examine the purple solution below.
What wavelengths of light are being absorbed? What colors of light
are being transmitted? Answer
