Lab Manual

When you apply a voltage across a tube of gas, the tube gives off light. The electricity excites the electrons in the gas atoms. When the electrons relax back to their original states, they release the extra energy––which is equal to the difference in the energies of the states––as light. The light released due to the transition from a higher to a lower energy state makes up the emission spectrum for that particular gas.

Electrons in atoms must be at discrete energy levels. Every element has a unique atomic structure, and the spacing of these electron energy levels is different for every element.

Therefore, each different element emits light at a particular set of energies. This leads to the formation of a discrete spectrum, which is a spectrum made up of distinct energies, each specific to the element that produced it. In other words, a discrete spectrum can be used to

fingerprint the presence of certain elements in a compound. Because energy is proportional to frequency, and frequency determines color, you see only a few distinct colors in the spectrum of each element. This unique set of colors can then be used to determine which element produced the emission spectrum.

Light can also be produced by heating an object. You may have seen this before when a very hot object appears to glow. This method of emission produces a continuous spectrum, so you can see some amount of all frequencies within a particular range. An example of this is a hot stove coil that appears orange because of the particular set of frequencies it emits. The hot coil actually emits a whole range of wavelengths throughout the infrared and visible parts of the electromagnetic spectrum.

Safety Precautions

Be very careful to not break the light bulb or spectral tubes to avoid broken glass.

Do not plug in light sockets until the light bulbs are completely screwed in to avoid the risk of electric shock.

Do not handle the spectrum tubes, power supply, or incandescent bulb with your bare hands after they have been used, since they will be extremely hot.

For this activity you will need the following:

Incandescent light bulb

Socket and plug for an incandescent bulb

Spectrometer

Spectrum tubes (neon, oxygen, nitrogen, helium)

Spectrum tube power supply

Thermal glove

Colored pencil set

For this activity you will work in pairs.