Electromagnetic radiation is one way that energy can travel through space. The microwaves, that heat up food, the light waves from a light bulb, that enable you to see or read after the sun has set, the television waves that bring the world into your home and the x-ray waves used to check for tuberculosis in the chest cavity are all a type of wave. Two of the units associated with waves are the wavelength and the frequency. The wavelength (l , lambda ) and the frequency (n , nu) of this radiation are related to the speed of light ( c ). The product of the wavelength (l ) and the frequency ( n ) is equal to the speed of light ( c ) , or ( l· n ) = c .

If an atom or a molecule can pick up just enough energy to go from its lowest energy state to the next higher Energy State it will do so. Now it is in the higher Energy State, where it is not as stable. It can give off this same amount of energy and return to its original state. The energy it gives off is the same as that which it picked up in the first place. Now if this energy is released as specific amount that can be seen by the naked eye then you will see that energy as visible light.

As with all things this is a very simple example. In reality things look a lot more complicated, but even in this more complex situation it is composed of these simple steps.

What is being moved by the energy put in or is moving when energy is released is the electron. Consider an atom with just one electron (this would be the Hydrogen atom) starting with the least (or lowest) energy. Consider this energy as being the lowest rung (or step) of a ladder. Above it are other rungs representing higher energies. Lets look at a ladder with only 5 rungs.

We have to do one more thing with this ladder so that it will correctly represent the energy levels (rungs) in the atom; the rungs are not equal spaced. As you go up (increasing energy) the rungs get closer together. Lets use the following diagram for a hydrogen atom (the values used are not the real values).
 

20 J		In this ladder of increasing energy the
19 J		only values the single electron can have are
18 J		1, 10, 16, 19 and 20 J (J = Joules = energy unit)
17 J		If you start having 1 J with the one electron of energy
16 J		what you will find is that if you add less than
15 J		exactly 9 J of energy, nothing happens.
14 J		The electron stays where it is. When exactly 9 J are
13 J		added the electron can go up to the next higher
12 J		energy level (rung). However, if you add a little more
11 J		than 9 J, again nothing happens. The electron can not
10 J		take out 9 J to move to the higher level leave and
9 J		the extra energy. Its the exact value or nothing (very
8 J		similar to exact change). Now, with the electron at the
7 J		10 J level, if you add exactly 6 J the electron can
6 J		move up to the next higher energy level. If the electron
5 J		is at the 10 J level and 9 J of energy is available, the
4 J		electron could move directly to the 19 J level. It does
3 J		not have to stop at the 16 J level first. This is what
2 J		happens when you add energy.
1 J

Now let's look at the process when the electron gives off energy. Let's start with the electron at the 19 J level. The following things can happen.

A - The electron gives off 18 J of energy all at once and end at the 1 J level

B - The electron gives off 9 J of energy and ends on the 10 J level, from there it can then give off another 9 J of energy and the electron ends at the 1 J level .

C - The electron gives off 3 J of energy and ends on the 16 J level, from there it can give off 15 J of energy and end at the 1 J level.

D - The electron gives off 3 J of energy and ends on the 16 J level, from there it can give off 6 J of energy and reach the 10 J level and finally give off 9 J of energy and end at the 1 J level.

The amounts of energy given off are: 18 J, 15 J, 9 J, 6 J and 3 J. These are the energies we could see if all these energies corresponded to wavelengths in the visible region of the spectrum. This would mean you would see five different lines in the spectrum. If two of the wavelengths are close to one another the spectral lines may appear as two lines or only one line (the two lines overlap).

Note: The pattern of adding the energy to the electron was D. The other three patterns also would be possible. It also means that the more possible energy levels the more transitions can occur and the more spectral lines can occur.

In this experiment you will be looking at the spectra of hydrogen gas, neon gas, helium gas and mercury vapor. You will also be doing the flame tests for sodium chloride, calcium chloride, potassium chloride, strontium chloride, barium chloride and lithium chloride.

Equipment:

Hand held spectroscopes, transformer, gas tubes (hydrogen, helium, neon and mercury vapor), nichrome wire, cobalt-blue glass plate, spot test plate. Bunsen burner with rubber hose.

Chemicals:

Solutions of: :Sodium chloride, calcium chloride, potassium chloride, strontium chloride, barium chloride, lithium chloride, and hydrochloric acid.

Procedure:

Part I. Obtain a transformer, the four gas tubes and a hand held spectroscope. Your instructor will show you how to safely set up and use the transformer with the different gas tubes as well as how to use the spectroscopes. Observe the spectra of each of the gases. Write down the number of different colors you see (please: bright red, crimson red, burgundy, blood red, scarlet, etc. are all red; do not worry about shades) and compared these with the overall color you see. You may want to indicate the number of lines you see for each major color. Please restrict youself to the six basic colors: violet, blue, green, yellow, orange, and red.

Part II. Obtain a spot test plate and place 3-4 drops of each of the different solutions into a depression. Place 1 mL of the hydrochloric acid into a depression. Use a grease pencil marker to label what is in each depression. Light the Bunsen burner (again your instructor will demonstrate the proper procedure). Take a nichrome wire and heat the end in the hot portion of the flame, so that the wire glows red and no colored flame is present. While the wire is still hot, dip it into the hydrochloric acid solution and reheat the wire in the flame. If a colored flame appears, continue to heat the wire and repeat the dipping of the wire into the hydrochloric acid solution. Reheat the wire. Continue this procedure until you get no colored flame when you reheat the wire. The wire is now clear (clean) of those substances that give a colored flame.

Dip the wire into one of the solutions and reheat it in the flame of the burner and observe if you get a colored flame, and if you do what color it is. You may also want to look at the flame through the spectroscope to observe how many lines and what colors these lines are for the element present in the solution. Hint: the chloride ion gives no color. Record the colors of each of the flames of the different solutions. Second hint: some of the solutions may have different shades of the same basic color; scarlet vs. burgundy.

You may want to look at the overhead fluorescent lights. Their spectrum is a continuous spectrum (shows all the wavelengths of all the colors) but super imposed on it is the spectrum of the element in the bulb that is needed to get the bulb started. This is mercury. It is also why the disposal of fluorescent bulbs is a serious business that can lead to high monetary fines.