In addition to the resources below, you may want to browse the chemistry textbooks in the Clemens Library, QD 31 - QD 33
Credo, Gale, and Oxford offer reference collections that let you cross-search many dictionaries and encyclopedias at once!
Not sure if it's okay to use Wikipedia or a web search as a starting point for your research? Check with your instructor or a librarian!
For an overview of the issue, check out Wikipedia's Citing Wikipedia article!