1. Molecules are made up of atoms linked together by sharing electrons.
2. Electrons in atoms and molecules are very restricted as to their energy, occupying only certain fixed (for any given atom or molecule) energy levels. This is somewhat like stairs in that you can occupy the level of a stair but not any level in between.
3. When electrons are spread out over many atoms, the energy levels (steps or stairs) become closer together.
4. The electrons in atoms and molecules can jump up energy levels if exactly the right amount of energy is supplied. This amount of energy can be provided by electromagnetic radiation. Visible light is one form of electromagnetic radiation.
5. Small molecules, with little spreading out of electrons, have large energy steps and so require electromagnetic radiation of higher energy than visible light. Consequently visible light passes through such molecules and they appear transparent.
6. For larger molecules, if the electrons are spread out enough in the molecule, the energy levels for the electrons are close enough together that visible light has enough energy to make the electrons jump up a level. When this happens, the particular energy of light, which corresponds to a particular wavelength or colour, is absorbed and disappears. The remaining light, lacking this colour, shows the remaining mixture of colours as non-white light.
7. For molecules to spread electrons out enough to absorb visible light, several double bonds (=) must be present alternating with single bonds (-). In all the following structures you will note this one phenomenon.
One note: a hexagon with a circle in it also represents a spreading out of electrons round the ring.
|1. Allura Red AC||Red #40||Orange-red||507 nm|
|2. Brilliant Blue FCF||Blue #1||Bright blue||630 nm|
|3. Erythrosine||Red #3||Cherry red||530 nm|
|4. Fast Green FCF||Green #3||Sea green||625 nm|
|5. Indigotine||Blue #2||Royal blue||608 nm|
|6. Sunset Yellow||Yellow #6||Orange||480 nm|
|7. Tartrazine||Yellow #5||Lemon yellow||426 nm|
Approximate wavelengths of coloured light (nm):
Violet: 400; blue: 450; green: 500; yellow: 580; orange: 620; red: 700.
US Food and Drug Administration (1993)
Ditto: Background for Consumers
Overview and Analysis
Chronology of Food Additive Regulations
Red #3 and other Colorful Controversies
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