Citations

1. The Usborne Illustrated Dictionary of Chemistry.
London, England: Usborne Publishing Ltd, 2000.

2. Helium. January 28, 2008.
<http://periodic.lanl.gov/elements/2.html >.

3. It's Elemental: Helium. January 28, 2008.
<http://education.jlab.org/itselemental/ele002.html >.

4. Helium. January 28, 2008.
<http://www.webelements.com/webelements/scholar/elements/helium/uses.html >.

5. Helium(He). January 30, 2008.
<http://www.lenntech.com/Periodic-chart-elements/He-en.htm >.