Quantum Mechanics, Electromagnetic Radiation, Waves and Particles

Unit Information

This unit corresponds to the material covered in chapter 10 in the text. Additionally, there is a reading about color and light which contains information you must know.

Waves and Quantum Mechanics packet − does not include the reading on colors and light.

Get used to the electromagnetic spectrum. I am going to ask that whenever you perform a frequency/wavelength/energy problem that you identify the type of electromagnetic radiation being described.

Electromagnetic Radiation
In the simplest sense, electromagnetic radiation (emr) is any type of energy that meets two criteria. The first is that it can be thought of as a wave/particle. The second is that it travels at the speed of light. Sound is not emr. While it travels as a wave, it is a pressure wave which does not have the same consistent wavelength/frequency features that types of emr have. Secondly, it is not energy. Lastly, it moves considerably slower than the speed of light. Visible light, infrared and ultraviolet light (both are invisible to humans), microwaves, X-rays, and gamma rays are also different types of emr. For a more extensive list, consult the table in your packet.
	The spirit of radio − it's more than just a song by Rush; it's wavelength, frequency, and energy.

Speed of Light

The speed of light, 2.998 × 10⁸ m/s, is remarkably fast for anything that takes place on Earth. However, when dealing with interplanetary distances, the speed of light can be used to show how far apart celestial objects are.

Let's say you decide to call a friend (cell to cell) who lives 10 miles away. The waves will require 5.366 × 10^-5 s to travel between the phones. To put this in perspective, your eyes take no faster than 150 ms (1.50 × 10^-3 s) to blink. The cell phone waves are traveling roughly 350 times faster than this.

Maybe you will have a friend who lives on Pluto one day. How long would it take cell phone waves to reach Pluto? The mean distance between Pluto and Earth is 5.666 × 10¹²m. If you divide this distance by the speed of light you will find that it takes 18894 s, or 5 h 14 m 54 s for your words to reach your friend on Pluto. This means that upon

"This is the United States calling are we reaching?" No, your call was dropped somewhere around Mars.

pressing the "Send" button on your phone, it would take 5 h 14 m 54 s before your friend's phone began to ring. Consequently, when your friend answers and says "Hello" it will take another 5 h 14 m 54 s for the greeting carried on those cell waves to reach you back on Earth.
When reporting on the Columbia shuttle tragedy, CNN made the mistake of reporting that the shuttle was traveling nearly 18 times the speed of light. This is impossible as the speed of light is considered "the speed limit of the universe" and nothing can travel faster than light, or more appropriately, electromagnetic radiation.

The Color of Stars
The color of stars is important on two fronts. First, it can tell us a great deal about the chemical composition of the star. Secondly, the color of the star can tell us the approximate temperature of the star. The second point is actually more a function of the first, as will be explained later.
Stars are essentially very hot balls of gas. When they are viewed through a diffraction grating (like the glasses we wore in the lab) the star's light is diffracted, or broken down into its component wavelengths. Studies of individual gases like we did in the lab have provided astronomers with information about the wavelength, intensity, and the number of lines of each color emitted by the gas. When stars are viewed in this same way, the components combined spectra will be seen. Since certain wavelengths are unique to certain gases, the presence of certain wavelengths can confirm the presence of a certain element. The color of a star can also give insight into its temperature. Let's say that a certain electron transition gives a wavelength of light that corresponds to yellow. Now let's say that the temperature of that star is increased. This will excite the electron to higher energy levels than before. As a result, when the electron returns to a lower energy level, a higher energy color (and shorter wavelength) will be seen. In conclusion, it can be said that stars that appear red have the lowest temperature whereas stars that appear violet have the highest temperature. Our sun (it's actually orange when viewed from above the atmosphere) is a cooler star, checking in at a modest 5000 or 6000 degrees Celsius. Violet stars are perhaps four times hotter.
	Sorry Vincent, this is the real Starry Night.

Aurora
	Aurora is a generic term for the ribbon-like colored lights that are often seen near Earth's poles. Solar winds blow a great deal of radiation towards Earth. These particles (recall that alpha and beta particles are charged) congregate near the Earth's poles due to their magnetic field. As they hit atoms in a region of the atmosphere called the Van Allen belt, electrons are ejected from atoms. When these electrons collide (and join) a new atom, photons of light are emitted. The high concentration of oxygen and nitrogen in the atmosphere, in conjunction with the energy of the electrons, generally produce red or green colored lights. When seen in the northern atmosphere, this is referred to as aurora borealis (northern lights). In the southern hemisphere, the term aurora australis (southern lights) is used.
Collective photons − Heaven let your light shine down

1927 Solvay Conference
There is some excellent footage of the participants of the 5^th Solvay Conference from a site that is actually pushing a book about Max Born. The clip is available as a Flash clip and as a Real Player clip. Most people don't realize that conferences at Solvay (an institute in Brussels) were held periodically before 1927 and since then to the present. It is a venue for the world's elite chemists and physicists to gather and share/discuss ideas. Remarkably, I have yet to be invited. Still, the photograph from the 1927 conference is famous because of the magnitude of the names present. Many of them are household names, and most others are considered among the founding fathers of quantum mechanics. Interestingly many of them were not well known in their day.
	The 1927 Solvay Conference − They would own you on Jeopardy!

Orbitals

Erwin Schrödinger's wave equation is used to describe the probability of finding an electron in a certain region of space. The region of space is called an orbital and is defined largely by the energy that the electrons within it possess. Orbitals are NOT solid objects, but rather three-dimensional regions of space that coexist in the same space. Think of orbitals coexisting with each other like multiple boundary lines for different sports on the same playing field. Depending on the sport you play, there will be a certain boundary line that is understood by the players to keep the ball "in play." The ball can pass the boundary lines at certain moments, just as an electron can be outside a particular orbital at a give moment. The orbital only gives a region of 90% probability, that is to say there is a 90% chance of finding a certain electron within the orbital defined by its energy.

Orbital Viewer is a nice tool that generates the shapes of orbitals that are observable (e.g. 1s or 4p) and those that are not observable (e.g. 8s or 4g). There is a nice chart that shows the basic shapes of all these orbitals (up to n = 10). A separate small download is needed if you want to render the orbital shapes and rotate them around on your own.