NATS 1870 Lecture Notes - Lecture 5: Covalent Bond, Carotene, Phosphorescence
19 Nov 2014
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Document Summary
Structure and spacing of energy levels is key for color. There are particular structures within molecules that tend to absorb visible(380- 700nm)wavelengths to give rise to a colored object (to the human eye) Example: double covalent bond (have equal sharing of electrons) Single covalent bond (hold electrons quite tightly)- in order for an electron to jump to a higher energy level, they need to absorb a lot of energy, like ultraviolet, in this case a substance would be colorless. With double covalent bonds, the first bond is held tightly but the second set of electrons are primed to absorb visible wavelengths. A lot of dyes and pigments have double covalent bonds. 3 important dyes in chemistry: violet, matter red & yellows/oranges. Example: auxochromes - when groups of atoms are added to a colorless substance and they end up changing the energy level spacing; this changes the wavelengths that get absorbed, the opposite wavelengths will give the substance its color.
