Ask A Scientist Chemistry Archive

Question:  What determines the colors which a substance will reflect?  There must be some relationship between the chemical structure of a molecule and the
color of that substance.  Can someone give a simple explanation of this?
ghodel

Answer:  It's exactly the chemical structure of the molecule that determines the
color of the solution.  In organic molecules, it's usually the conjugation
of double bonds (single bond-double bond-single-double, etc) that accounts
for color.  These bonds absorb certain wavelengths of white light thereby
transmitting others thus giving off a color.  For inorganics (the reason
why copper solutions are blue in water), its the bonds again that absorb
certain wavelengths and transmit others.  The copper-water bond absorbs
light in the 580-600 nanometer range (yellow-orange) so it transmits
blue light.  A yellow solution then absorbs blue light(450 nanometers).
-Joe Schultz