http://en.wikipedia.org/wiki/Oxygen

http://www.radiochemistry.org/periodictable/elements/8.html

http://education.jlab.org/itselemental/ele008.html

http://www.chemistryexplained.com/elements/L-P/Oxygen.html

http://www.webelements.com/oxygen/

http://periodic.lanl.gov/elements/8.html

http://www.answers.com/topic/oxygen

http://www.3rd1000.com/elements/Oxygen.htm

http://www.chem4kids.com/files/elements/008_speak.html

http://chemistry.about.com/od/elementfacts/a/oxygen.htm