How does electron confinement in an ion or molecule affect its color?

Answer 1

I assume that electron confinement here refers to the act of preventing an electron from getting excited (gaining more energy).
When electrons are unable to gain or lose energy, they will not be able to release photons that coincide with the wavelengths of the different colours of light. Therefore, the ion or molecule will appear colourless.
Basically, the idea is that electrons need to get excited first, then release all this energy that it just received (in photons) which coincides with a particular range of energy level similar to a particular colour of light. More energy received and released means it will coincide with shorter wavelength colours, and vice versa.

Answer 2

The more electrons are confined, the closer the spacings between their energy levels and so the bluer the colors they absorb. Different ions obviously confine their electrons differently, and so have different colors. Turning water into wine is a classic magician's trick. The magician taps the edge of a glass of water with a wand and quickly pours it into an empty wine glass, and voila! The water is instantly changed into red wine. Pouring the wine into a third container changes it back into water.

Professional magicians sometimes use a pitcher or carafe with a hidden compartment to create the illusion. But anyone who has done an acid-base titration in freshman chemistry knows a simpler way to do the trick that is just as convincing- so long as no one insists on tasting the "wine" or the "water".

Fill a glass with water. Make the water slightly alkaline by adding a few drops of sodium hydroxide solution.
Hide a few drops of phenolphthalein solution in the bottom of a wine glass. Phenolphthalein is an organic compound that is colorless in acidic and neutral solution. It has an intense red color in alkaline solution.
Pour the alkaline water into the wine glass to convert the phenolphthalein to its red form.
Hide a few drops of a concentrated acid in the bottom of a third glass. When the "wine" is poured into this glass, the acid neutralizes the base, and the phenolphthalein is converted back into its colorless form.
But knowing how to do the trick doesn't make it any less mysterious. Just why the color change occurs when the pH changes is the subject of this article.
Since color change often accompanies chemical change, you might suspect that a chemical reaction is responsible for indicator action. This indeed the case. Indicators are weak acids or bases with differently colored acid and base forms.
The indicator reaction is pH dependent because it involves either the release or capture of hydrogen ions:

HIn H+ + In-


where "HIn" and "In" stand for the indicator molecule with and without an attached hydrogen ion.
The two forms of the indicator molecule have noticeably different colors. For example, bromocresol green has a yellow HIn form and a blue In form. When there are equal amounts of HIn and In, the solution looks bright green. Adding a drop of acid adds H+ ions which react with the In- ions to form HIn, and the solution becomes more yellow. Adding a drop of base converts HIn to In, and the solution becomes more blue.

But what exactly does attaching a hydrogen to the molecule do to cause a color change? To understand the answer, we'll have to know a little about how color and molecular structure are related.

Light delivers energy in little packets called photons. Different colors of light pack different amounts of energy in their photons. For example, photons of violet light have almost double the energy of those of red light. Different molecules absorb different colors of light, depending on their electronic structure.

All materials absorb photons of some energy. But only substances that absorb photons of visible light will have color. Molecules are very selective about what photon energies they will and will not absorb. In fact, the photon energies a molecule will absorb are so characteristic that they can be used as a 'fingerprint' to identify that molecule in a mixture. This preferential absorption can be explained by assuming that molecules have quantized energies; that is, they exist only in certain allowed energy states.

Quantum theory shows how quantized energies arise naturally from the wavelike behavior of confined electrons. The photon will be absorbed only if its energy is exactly what is needed to take the molecule from one allowed state to another.
Since different molecules have different colors, it follows that molecular structure has something to do with the size of the energy transitions associated with absorption of visible light. The relationship is complex, but a simple model can be used to show many essential features. An electron bound in a molecule (or part of a molecule) is treated as though it is trapped in a uniform box with walls it cannot penetrate. This "particle in a box" model shows that confining electrons in a smaller space tends to make energy level spacings larger. The model shows that electrons restricted to a box the size of a covalent bond absorb in the ultraviolet, and so are colorless. Electrons that can spread over many atoms within a molecule absorb photons of lower energy, and if the box length is just so (a bit over 0.6 nm, and a bit less than 0.8 nm, according to the model) they'll absorb visible light. This explains why many organic materials that have color have structures with electrons that aren't pinned down in single covalent bonds.


See Why things have color from Carnegie-Mellon for a Java applet that illustrates how electron confinement affects the color of a material. Confining electrons to a smaller space makes the light they absorb bluer.
While many other factors can come into play, we have a general principle to guide our examination of indicator structures: Color changes can be caused by changes in electron confinement. More confinement makes the light absorbed bluer, and less makes it redder.
When a hydrogen ion combines with the base form of an indicator molecule, it will confine two formerly mobile electrons to a single covalent bond with the hydrogen, shifting the light that is absorbed towards the blue end of the spectrum. Indicator structures often undergo additional changes that amplify the change in electron confinement.

The color of a transparent object is due to the colors of light that can pass through the material. For example, white light passing through a glass of red wine looks red because the wine has absorbed the other colors, and lets only the red light pass through. To see this, try looking through a piece of red cellophane at objects of different colors. All colors but red vanish. Non-red objects become dark, with blue-green objects becoming areas become almost black- the cellophane absorbs light with these colors. The red areas still look red- red light is not absorbed. The color of a solution comes from the light it doesn't absorb.
The color most strongly absorbed is the complement of the color that passes through the material. A solution that appears sea green absorbs red light; a purple solution absorbs green light.

Answer 3

color is produced by jumps in energy normally involving tranistion metals. the more energy released the more intense the color.