I'm So Excited, and I Just Can't Hide It
As we talked about last time, there are 15 causes of color, broken down into 5 classifications. This week we're going to talk about Vibrations and Excitations which includes:
- Gas Excitations
- Vibrations and rotations
Electrons live in specific energy levels, based on how far they are from the atom's nucleus. The more energy the electron has, the farther away from the nucleus the electron lives. Imagine a ladder, with each rung representing an energy level, and electrons spaced out on all of the rungs. If an electron on the bottom rung were to absorb some energy, it would move up a rung. However, electrons are quite fond of their "home" rung and will usually look to get back to it. In order to do this, the electron must release the energy it absorbed when it moved up a rung. Depending on the wavelength of this released energy it may be heat, or light in the visible spectrum. As usual, this is a gross oversimplification of the process and there is so much fantastic information on the nature of matter that I could post from here until doomsday and never touch it all. Such is the awesome nature of science!
Take a gas, say, oh, I don't know, neon. Put it in a glass tube, bend the tube so that it says "Budweiser" and then run a current through the gas in the tube, and what do you get? A nice orange color and a cool sign for your bachelor pad that will be the first thing to go once your significant other moves in with you.
This is a prime example of what we mentioned before. If you excite the electrons in the gas, in this case by introducing an electric current, they'll jump up an energy level, and then, when coming back down, they'll emit radiation in the visible spectrum. The color that's produced is dependent on the gas, and, for some gases, dependent upon the strength of the current. Neon is reddish orange, Helium is whitish, Argon is bluish and Krypton was destroyed with Kal-El's family. Kidding. It's actually somewhat gray. What is important to note, is that it's not as if energized neon "makes" the color red. It simply emits radiation with a specific wavelength. When this radiation strikes the receptors in your eyes, it is perceived as the color red. If evolution (or intelligent design if you choose to swing that way) had gone another route, red might be blue. How does that bend your noodle?
Gas excitations is also the reason behind the colors of the Northern Lights. Charged particles from the sun are directed along the Earth's magnetic fields to slam into gases in the atmosphere at the poles. This collision causes energy in the visible spectrum to be emitted and we see them as auroras.
Incandescence works in the same way as gas excitations, only instead of a noble gas that a current is passed through, we're passing a current through a conductor, but a conductor that allows for some resistance to the electron flow. A basic light bulb consists of a filament in a glass bulb that had the oxygen removed. Current flows through the filament, but is somewhat impeded, based on the material the filament is made of. This in turn excites the electrons, causing them to, say it with me, jump up an energy level. When they return, they emit radiation in the visible spectrum. The reason that oxygen is removed from the bulb, is that the filament gets quite hot in this case, and if the bulb were filled with oxygen, the filament would burst into flame before doing that which it was made to do.
Incandescence also describes why hot things glow reddish. All objects, including your bad self, absorb and emit radation. Most of this radiation is emitted in the non-visible spectrum, usually the infrared spectrum, also known as heat. This is why your couch is warm to the touch after a marathon American Idol watching session. Your body emits infrared radiation (heat) as you sit. It is absorbed by the couch, which then emits it once you leave. Similarly, if you were to turn on an electric burner, and hold your hand above it, your hand gets warm as it absorbs the infrared radiation released by the burner. As the burner gets hotter, and the electrons get more and more excited, the burner will begin to emit radiation in the visible spectrum, and it gets red. This is also why, for anyone who has ever placed their hand on a hot burner, the color red is considered a "hot " color. After all, in order for your burner to emit radiation in the visible spectrum, it first had to work on through the infrared spectrum, and that spectrum is a mite toasty.
Thermal imaging allows us to "see" objects based on the thermal radiation they emit, which is what will allow the SWAT team to nail your pasty ass should you decide to go all postal and hole up in your compound. It's also quite effective for intergalactic big game hunters.
Vibrations and Rotations
What color is water? Depends right? If you were to look at a glass of water, it'd be clear. Look at a river, and it's kind of a brownish-green. Look at an ocean in the Caribbean and it's pale blue. The fact is, is that water is blue, but not for the reasons you might think.
This is the part of the post that I have the least amount of understanding of, so please bear with me. Water molecules are composed of hydrogen and oxygen, all bonded together in nice springy molecules. As the isolated molecules come together in water, or in ice, the vibrations of these molecules are increased so that these vibrations can interact with light in the visible spectrum by way of absorbing the red portion of light. As a result, water appears to be a light shade of blue. So, why does a glass of water appear as clear, rather than blue? It's because there isn't enough water in the glass for this effect to take place. In order for light to be absorbed by water's vibrations, you need either large body, such as a lake or an ocean, or small body just extended along a long axis, as in a tube. When you see a blue ocean, part of the blue may be scattering as a result of particles in the water, some may be a reflection of the blue sky, depending on your angle of view, but some is the absorption of red light by the vibrations of water's molecules. You can see an example of blue water in a clear tube in this excellent article by the fine folks over at Dartmouth. It's a tough read, but very interesting if you take the time.
There we go. One fifth of the way done, and we've all survived thus far. Good science is any science you can walk away from, I always say. Next week we tackle the joy that is the Ligand Field Effect. Can you feel the excitement? It's palpable. I can so totally palp it.
Encyclopedia Britannica - Vibrations and Rotations
Why is Water Blue? - Charles L. Braun and Sergei N. Smirnov, Department of Chemistry Dartmouth College
Wikipedia - Gas discharge
Encyclopedia Britannica - Gas excitation
Wikipedia - Incandescence
SPi - Thermal Infrared Blackbody Thermography
Wikipedia - Blackbody