Atomic Spectra
Chemistry Laboratory
Honors Chemistry (820), 2017-18


Last update: Thursday, October 25, 2007 10:46 AM


In this experiment you will observe light from various sources and learn how to distinguish between a continuous spectrum and a line spectrum.


In 1853, the scientist Anders Angstrom passed a current through a sealed tube filled with hydrogen gas. When he viewed the resulting light through a prism he saw a line spectrum. This was one of the first clues that the atom possessed an internal structure. Later on, Bohr devised a model of the atom that explained the line spectrum of hydrogen. In this experiment, you will view the line spectrum of hydrogen and other elements using a spectroscope. Each element has its own characteristic pattern of spectral lines. The uniqueness of each element’s line spectrum serves as an “atomic fingerprint” that identifies an element.

A spectroscope is an instrument that separates light by diffraction according to its wavelength. The light enters a narrow slit and hits a diffraction grating, where it is separated into the colors it contains. When you look through the spectroscope you see the different colors of light displayed. The spectroscope has a scale on it that allows you to measure the wavelength in nanometers (1 nm = 10–9 m). A continuous spectrum has all wavelengths of light. When viewed through a spectroscope, a continuous spectrum looks like a smooth rainbow of colors. In contrast, a line spectrum only has certain wavelengths of light. When viewed through a spectroscope a line spectrum looks like a set of distinct colored lines.


Be certain that you can identify the equipment and reagents listed below, before starting the experiment.

Safety and Waste Management

The gas discharge tubes (gas filled bulbs) get very hot. Be careful not to touch hot discharge tubes.


Go to each station and use a spectroscope to view the light from the light sources. Record your observations on the data sheet. Use the colored pencils to indicate the colors that you see.

Pre-activity Questions

Answer the following pre-activity questions. Record your answers in your laboratory notebook, or on the available report form according to the instructions from your teacher

  1. What is a spectroscope?
  2. What is a continuous spectrum?
  3. What is a line spectrum?
  4. What is a wavelength?
  5. What is a nanometer?
  6. What is the difference between the different parts of visible light (ROYGBIV)?



Record measurements for each day as indicated either in your laboratory notebook, or on the report form provided per the instructions of your teacher.

Post-activity Questions

Answer the following questions either in your laboratory notebook or on the post-activity question sheet supplied according to the instructions from your teacher.

  1. Describe a continuous spectrum. List all the sources that gave a continuous spectrum.
  2. Describe a line spectrum. List all the sources that gave a line spectrum.
  3. When the lamp for the gas filled bulb was turned on, why did it light up? Be sure to use these terms: electron, energy, ground state, excited state
  4. What is a photon and how does it relate to the line spectra of elements?
  5. What do the unique line spectra suggest about the electron arrangement of atoms of various elements?
  6. Below are wavelengths (in nm) of light emitted by Hydrogen.
  1. Sketch where the lines would appear on a nanometer scale like the one shown below.
      0    100  200  300  400  500  600  700  800  900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
  2. For the first line in each series, calculate the frequency in Hz.
  3. For the first line in each series, calculate the energy in kJ/mol.


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